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All Textbook Solutions for Conceptual Physics: The High School Physics Program
Why is physics the most basic science?Why is mathematics important to science?What are the steps of the scientific method?Is a scientific fact something that is absolute and unchanging? Defend your answer.Scientific theories undergo change. Is this a strength or a weakness of science? Defend your answer.What does it mean to say that if a hypothesis is scientific, then there must be a means of proving it wrong?How do science and technology differ?How are science and the arts similar?How do science and religion differ?Why do citizens have a responsibility to have some basic understanding of natures rules?How does the rate of change of progress differ today from the rate in previous centuries?Why does science tend to be a self-correcting' way of knowing about things?What is likely being misunderstood by someone who says, 'But thats only a scientific theory'?a. Make an argument for halting the advances of technology. b. Make an argument for continuing advances in technology. c. Contrast your two arguments.What is the difference between force and net force on an object?What is the net force on a box that is being pulled to the right with a force of 40 N and pulled to the left with a force of 30 N?What name is given to the stretching force that occurs in a spring or rope being pulled?What two quantities are necessary to determine a vector quantity?How does a vector quantity differ from a scalar quantity?Give an example of a vector quantity. Give an example of a scalar quantity.How much tension is in a rope that holds up a 20-N bag of apples at rest?What does F=0 mean?What is the net force on an object at rest?10AWhat is the angle between a support force and the surface on object rests upon?What two forces compress a spring inside a weighing scale when you weigh yourself?When you are at rest and supported by a pair of weighing scales, how does the sum of the scale readings compare with your weight?Can an object be moving and still be in equilibrium? Defend your answer.If you push a crate across a factory floor at constant speed in a constant direction, what is the magnitude of the force of friction on the crate compared with your push?16AAccording to the parallelogram rule for two vectors, what does the diagonal of a constructed parallelogram represent?Consider the suspension of Nellie in Figure 2.11. Name the three forces that act on her. What is your evidence that they cancel to zero?Consider Nellie in Figure 2.12. What changes in rope tension occur when the ropes make a greater angle with the vertical?When Nellie hangs from ropes at different angles, as shown in Figure 2.13, how does the vector resultant of the two rope tensions compare with her weight?Blocks A and B are supported by the table. Block C is partly supported by the table and partly by the rope. Rank the support forces provided by the table from greatest to least.In the diagram below, identical blocks are suspended by ropes, each rope having a scale to measure the tension (stretching force) in the rope. Rank the scale readings from greatest to least.Burl and Paul stand on their sign-painting scaffold. Tension in the left rope is measured a scale. Rank the tensions in that rope from greatest to least.Percy does gymnastics, suspended by one rope in A and by two ropes in positions B, C, and D. Rank the tensions in the ropes from greatest to least.A cat lies on the floor. Can you say that no force acts on the cat? Or is it correct to say that no net force acts on the cat? Explain.Consider two forces, one having a magnitude of 20 N and the other a magnitude of 12 N. What is the maximum net force possible for these two forces? The minimum?When a box of chocolate bars is in mechanical equilibrium, what can be correctly said about all the forces that act on it? Must the net force necessarily be zero?Faina says that an object cannot be in mechanical equilibrium when only a single force acts on it. Do you agree or disagree?Phyllis Physics hangs at rest from the ends of the rope, as shown at right. How does the reading on the scale compare to her weight?Harry the painter swings year after year from his bosuns chair. His weight is 500 N and the rope, unknown to him, has a breaking point of 300 N. Why doesnt the rope break when he is supported as shown at the left? One day Harry is painting near a flag-pole, and, for a change, he ties the free end of the rope to the flagpole instead of to his chair as shown at the right. Why did Harry end up taking his vacation early?How many significant forces act on a your physics book when it is at rest on a table? Identify the forces.Why doesnt the support force that acts on a book resting on a table cause the book to rise from the table?Nicole stands on a bathroom scale and reads her weight. Does the reading change if she stands on one foot instead of both feet? Defend your answer.Justin sets a hockey puck sliding across the ice at a constant speed. Is the puck in equilibrium? Why or why not?Alyssa pulls horizontally on a crate with a force of 200 N, and it slides across the floor at a constant speed in a straight line. How much friction is acting on the crate?Consider a heavy refrigerator at rest on a kitchen floor. When Anthony and Daniel start to lift it, does the support force on the refrigerator provided by the floor increase, decrease, or remain unchanged? What happens to the support force on Anthonys and Daniels feet?Sneezlee is supported by two thin wires. Is the tension in each wire less than, equal to, or more than half his weight? Use the parallelogram rule to defend your answer.Sneezlees wire supports are repositioned as shown. How does the tension in each wire compare with the tension of the previous question?If a picture frame were supported by a pair of vertical wires, tension in each wire would be half the weight of the frame. When the frame is supported by wires at an angle, as shown below, how does the tension in each wire compare with that of vertical wires?A monkey hangs by a strand of rope and holds onto the zoo cage as shown. Since her arm holding the cage is horizontal, only the rope supports her weight. How does the tension in the rope compare with her weight?Why cant the strong man pull hard enough to make the chain perfectly straight?Two vertical chains are used to hold up a 1000-N log. One chain has a tension of 400 N. Find the tension in the other chain.Lucy Lightweight stands with one foot on one bathroom scale and her other foot on a second bathroom scale. Each scale reads 300 N. What is Lucys weight?Harry Heavyweight, who weighs 1200 N, stands on a pair of bathroom scales so that one scale reads twice as much as the other. What are the scale readings?The sketch shows a painters staging in mechanical equilibrium. The person in the middle weighs 250 N, and the tensions in both ropes are 200 N. What is the weight of the staging?A staging that weighs 300 N supports two painters, one 250 N and the other 300 N. The tension in the left rope is 400 N. What is the tension in the right rope?Two children push on a heavy crate that rests on a basement floor. One pushes horizontally with a force of 150 N and the other pushes in the same direction with a force of 180 N. The crate remains stationary. Show that the force of friction between the crate and the floor is 330 N.Two children push on a crate. They find that when they push together horizontally with forces of 155 N and 187 N, respectively, the crate slides across the floor at a constant speed. Show that the force of friction between the crate and the floor is 342 N.What were the two classifications of motion, according to Aristotle?According to Aristotle, what kinds of motion required no forces?What simple way of interpreting astronomical observations did Copernicus advocate?What were the consequences to Galileo for supporting the ideas of Copernicus?Who relied on experiment, Aristotle or Galileo?How did Galileo discredit Aristotles assertion that a force is needed to keep objects, moving?Galileo let a ball roll down one incline and then up another. Compared with its initial height, how high did the ball roll up the second incline?What name is given to the property of an object to resist changes in motion?Who was the first to consider the role of inertia, Galileo or Newton?What is the tendency of an object at rest when no forces act on it?What is the tendency of a moving object when no forces act on it?What relationship does mass have with inertia?What does it mean to say mass and weight are proportional to each other?When does an object with twice the mass of another weigh twice as much?What do you feel when you shake some-thing to and fro? What do you feel when you hold it against the pull of gravity?What is the standard (or SI) unit of measurement for mass?What is the standard (or SI) unit of measurement for weight?What is the weight of a 1-kg brick?How fast are you moving relative to Earth when you are standing still? How fast are you moving relative to the sun?If you're in a smooth-riding bus that is going at 40 km/h and you flip a coin vertically, how fast does the coin move horizontally while in midair?Different materials rest on a table. a. From greatest to least, rank them by how much they resist being set into motion. b. From greatest to least, rank them by weight. c. From greatest to least, rank them by the support (normal) force the table exerts on them.The three pucks are sliding across ice at the noted speeds. Air resistance and ice friction are negligible. a. Rank them, from greatest to least, by the force needed to keep them going. b. Rank them, from greatest to least, by the force needed to stop them in the same time interval.If a woman has a mass of 50 kg, calculate her weight in newtons.Calculate in newtons the weight of a 2000-kg elephant.Calculate in newtons the weight of a 2.5-kg melon. What is its weight in pounds?An apple weighs about 1 N. What is its mass in kilograms? What is its weight in pounds?Susie Small finds she weighs 300 N. Calculate her mass.A bowling ball rolling along a lane gradually slows as it rolls. How would Aristotle interpret this observation? How would Galileo interpret it?When a ball rolls down an inclined plane, it gains speed because of gravity. When rolling up it loses speed because of gravity. Why doesnt gravity play a role when it rolls on a horizontal surface?Jacob gives his skateboard a push and it rolls across the classroom floor. Emily says that after it leaves Jacobs hand, his force remains with it, keeping it going. Sophia disagrees and says that Jacobs push gives the skate-board speed, not force, and that when his hand is no longer in contact the force is no more. Who do you agree with? Discuss this with your classmates.A space probe can be carried by a rocket into outer space. Your friend asks what kind of force keeps the probe moving after it is released from the rocket and on its own. What is your answer?In an orbiting spacecraft, you are handed two identical closed boxes, one filled with sand and the other filled with feathers. How can you tell which is which without opening the boxes?Many automobile passengers suffer neck injuries when struck by cars from behind. How does Newtons law of inertia apply here? How do headrests help to guard against this type of injury?Tim practices a demonstration before doing it for Sunday dinner. What concept is he illustrating, and why is he careful not to pull the tablecloth slightly upward?Suppose you place a ball in the middle of a wagon that is at rest and then abruptly pull the wagon forward. Describe the motion of the ball relative to the ground and the wagon.To pull a wagon across a lawn with constant velocity, you have to exert a steady force. Does this fact contradict Newtons first law, which tells us that motion with constant velocity indicates no force?When a junked car is crushed into a compact cube, does its mass change? Its volume? Its weight?If an elephant were chasing you, its enormous mass would be very threatening. But if you zigzagged, the elephants mass would be to your advantage. Why?When you compress a sponge, which quantity changes: mass, inertia, volume, or weight?Which has more mass, a 2-kg fluffy pillow or a 3-kg small piece of iron? More volume? Why are your answers different?Is it more accurate to say that a dieting person loses mass or loses weight?A massive ball is suspended on a string and slowly pulled by another string attached to it from below, as shown. a. Is the string tension greater in the upper or the lower string? Which string is more likely to break? Which property, mass or weight, is more important here? b. If the string is instead snapped downward, which string is more likely to break? Is mass or weight more important this time?The head of a hammer is loose and you wish to tighten it by banging it against the top of a workbench. Why is it better to hold the hammer with the handle down, as shown below, rather than with the head down? Explain in terms of inertia.As Earth rotates about its axis, it takes three hours for the United States to pass beneath a point above Earth that is stationary relative to the sun. What is wrong with the following scheme? To travel from Washington, D.C. to San Francisco using very little fuel, simply ascend in a helicopter high over Washington, D.C., and wait three hours until San Francisco passes below.45AA stone is shown at rest on the ground. a. The vector shows the weight of the stone. Complete the vector diagram showing another vector that results in zero net force on the stone. b. What is the conventional name of the vector you have drawn?Here a stone is suspended at rest by a string. a. Draw force vectors for all the forces that act on the stone, b. Should your vectors have a zero resultant? c. Why, or why not?Here a stone is being accelerated vertically upward. a. Draw force vectors to some suitable scale showing relative forces acting on the stone. b. Which is the longer vector, and why?Suppose the string in the figure in Question 48 breaks and the stone slows in its upward motion. a. Draw a force vector diagram of the stone when it reaches the top of its path. b. Is the net force on the stone zero at the top?Here is a stone sliding down a friction-free incline. a. Identify the forces that act on it and draw appropriate force Vectors. b. By the parallelogram rule, construct the resultant force on the stone (carefully showing it has a direction parallel to the incline—the same direction as the stones acceleration).Calculate your own mass in kilograms and your weight in newtons.A medium-size American automobile has a weight of about 3000 pounds. What is its mass in kilograms?What is the weight in newtons of an automobile with a mass of 1800 kg?If a woman weighed 500 N on Earth, what would she weigh on Jupiter, where the acceleration of gravity is 26m/s2?Gravitational force on the moon is only 1/6 that on Earth. What is the weight of a 10-kg object on the moon and on Earth? What is its mass on the moon and on Earth?Grandparents are interested in the educational progress of their grandchildren. Many have little science background. Its possible that relatives far back in your family tree believed that Earth was stationary in the center of the universe. Write a letter to Grandma or Grandpa. Tell what you've learned about a moving Earth and how a person who might be unsure of it could be convinced.How can you be both at rest and also moving about 107,000 km/h at the same time?You cover 10 meters in a time of 1 second. Is your speed the same if you cover 20 meters in 2 seconds?Does the speedometer of a car read instantaneous speed or average speed?Averagespeed=distance covered divided by travel time. Do some algebra and multiply both sides of this relation by travel time. What does the result say about distance covered?Which is a vector quantity, speed or velocity? Defend your answer.What two controls on a car cause a change in speed? What control causes only a change in velocity?What is the acceleration of a car moving along a straight-line path that increases its speed from zero to 100 Km/h in 10 s?By how much does the speed of a vehicle moving in a straight line change each second when it is accelerating at 2km/hs? At 4km/hs? At 10km/hs?Why does the unit of time enter twice in the unit of acceleration?What is the meaning of freefall?For a freely falling object dropped from rest, what is the instantaneous speed at the end of the fifth second of fall? The sixth second?For a freely falling object dropped from rest, what is the acceleration at the end of the fifth second of fall? The sixth second? At the end of any elapsed time t?How far will a freely falling object fall from rest in five seconds? Six seconds?How far will an object move in one second if its average speed is 5 m/s?How far will a freely falling object have fallen from a position of rest when its instantaneous speed is 10 m/s?What does the slope of the curve on a distance-versus-time graph represent?What does the slope of the curve on a velocity-versus-time graph represent?Does air resistance increase or decrease the acceleration of a falling object?What is the appropriate equation for how fast an object freely falls from a position of rest? For how far that object falls?Jogging Jake runs along a train flatcar that moves at the velocities shown. From greatest to least, rank the relative velocities of Jake as seen by an observer on the ground. (Call the direction to the right positive.)Below we see before and after snapshots of a cars velocity. The time interval between before and after for each is the same. a. Rank the cars in terms of the change in velocity, from most positive to most negative. (Negative numbers rank lower than positive ones, and remember, tie scores can be part of your ranking.) b. Rank them in terms of acceleration, from greatest to least.These are drawings of Same-size balls of different masses thrown straight downward. The speeds shown occur immediately after leaving the throwers hand. Ignore air resistance. Rank their accelerations from greatest to least. Or are the accelerations the same for each?A track is made of a piece of channel metal bent as shown. A ball is released from rest at the left end of the track and continues past the various points. Rank the ball at points A, B, C, and D, from fastest to slowest. (Again, watch for tie scores.)A ball is released from rest at the left end of three different tracks. The tracks are bent from pieces of metal of the same length. a. From fastest to slowest, rank the tracks in terms of the speed of the ball at the end. Or, do all balls have the same speed there? b. From longest to shortest, rank the tracks in terms of the time for the ball to reach the end. Or do all balls reach the end in the same time? c. From greatest to least, rank the tracks in terms of the average speed of the ball. Or do the balls all have the same average-speed on all three tracks?In the speed versus time graphs, all times t are in s and all speeds v are in m/s. a. From greatest to least, rank the graphs in terms of the greatest speed at 10 seconds. b. From greatest to least, rank the graphs in terms of the greatest acceleration. c. From greatest to least, rank the graphs in terms of the greatest distance covered in 10 seconds.Calculate your average walking speed when you step 1 meter in 0.5 second.Calculate the speed of a bowling ball that moves 8 meters in 4 seconds.Calculate your average speed if you run 50 meters in 10 seconds. Distance=averagespeedtimeCalculate the distance (in km) that Charlie runs if he maintains an average speed of 8 km/h for 1 hour.Calculate the distance you will travel if you maintain an average speed of 10 m/s for 40 seconds.Calculate the distance (in km) you will travel if you maintain an average speed of 10 km/h for 1/2 hour. Acceleration=changeofvelocitytimeintervalCalculate the acceleration of a car (in km/h/s) that can go from rest to 100 km/h in 10 s.Calculate the acceleration of a bus that goes from 10 km/h to a speed of 50 km/h in 10 seconds.Calculate the acceleration of a ball that starts from rest and rolls down a ramp and gains a speed of 25 m/s in 5 seconds. From a rest position: Instantaneousspeed=accelerationtimeCalculate the instantaneous speed (in m/s) at the 10-second mark for a car that accelerates at 2m/s2 from a position of rest.Calculate the speed (in m/s) of a skateboarder who accelerates from rest for 3 seconds down a ramp at an acceleration of 5m/s2. Velocity acquired in free fall, from rest: v=gtCalculate the instantaneous speed of an apple 8 seconds after being dropped from rest.On a distant planet a freely-falling object has an acceleration of 20m/s2. Calculate the speed an object dropped from rest on this distant planet acquires in 1.5 s.A sky diver steps from a high-flying helicopter. If there were no air resistance, how fast would she be falling at the end of a 12-second jump? Distance fallen in freefall, from rest: d=12gt2Calculate the vertical distance an Object dropped from rest would cover in 12 seconds if it fell freely without air resistance.An apple drops from a tree and hits the ground in 1.5 seconds. Calculate how far it falls.Light travels in a straight line at a constant speed of 300,000 km/s. What is the lights acceleration?a. If a freely falling rock were equipped with a speedometer, by how much would its speed readings increase with each second of fall? b. Suppose the freely falling rock were dropped near the surface of a planet where g=20m/s2. By how much would its speed readings change each second?Which has more acceleration when moving in a straight line—a car increasing its speed from 50 to 60 km/h, or a bicycle that goes from zero to 10 km/h in the same time? Defend your answer.Correct your friend who says, 'The dragster rounded the curve at a constant velocity of 100 km/h.'What is the acceleration of a car that moves at a steady velocity of 100 km/h due north for 100 seconds? Explain your answer and state why this question is an exercise in careful reading as well as physics.Tiffany stands at the edge of a cliff and throws a ball straight up at a certain speed and another ball straight down with the same initial speed. Neglect air resistance. a. Which ball is in the air for the longest time? b. Which ball has the greater speed when it strikes the ground below?A ball is thrown straight up. What will be the instantaneous velocity at the top of its path? What will be its acceleration at the top? Why are your answers different?Two balls are released simultaneously from rest at the left ends of the equal-length tracks A and B as shown. Which ball reaches the end of its track first?Refer to the tracks in the previous problem. a. Does the ball on B roll faster in the dip than the ball rolling along track A? b. On track B, is the speed gained going down into the dip equal to the speed lost going up the dip? If so, do the balls then have the same speed at the ends of both tracks? c. Is the average speed of the ball on the lower part of track B greater than the average speed of the ball on A during the same time? d. So overall, which ball has the greater average speed? (Do you wish to change your answer to the previous exercise?)A dragster going at 15 m/s north increases its velocity to 25 m/s north in 4 seconds. What is its acceleration during this time interval?An apple drops from a tree and hits the ground in 1.5 s. What is its speed just before it hits the ground?On a distant planet a freely falling object has an acceleration of 20m/s2. What vertical distance will an object dropped from rest on this planet cover in 1.8 s?If you throw a ball straight upward at a speed of 10 m/s, how long will it take to reach zero speed? How long will it take to return to its starting point? How fast will it be going when it returns to its starting point?Hanna tosses a ball straight up with enough speed to remain in the air for several seconds. a. What is the velocity of the ball when it reaches its highest point? b. What is its velocity 1 s before it reaches its highest point? c. What is the change in its velocity during this 1-s interval? d. What is its velocity 1 s after it reaches its highest point? e. What is the change in velocity during this 1-s interval? f. What is the change in velocity during the 2-s interval? (Caution: velocity, not speed!) g. What is the acceleration of the ball during any of these time intervals and at the moment the ball has zero velocity?Kenny Klutz drops his physics book off his aunts high-rise balcony. It hits the ground below 1.5 s later. a. With what speed does it b. How high is the balcony? Ignore air drag.Calculate the hang time of an athlete who jumps a vertical distance of 0.75 meter.By any method you choose, determine your average speed of walking. How do your results compare with those of your classmates?You can compare your reaction time with that of a friend by catching a ruler that is dropped between your fingers. Let your friend hold the ruler as shown in the figure. Snap your fingers together as soon as you see the ruler released. On what does the number of centimeters that pass through your fingers depend? You can calculate your reaction time in seconds by solving d=12gt2 for time: t=2d/g. If you express d in meters (likely a fraction of a meter), then t=0.45d; if you express d in centimeters, then t=0.45d. Compare your reaction time with those of your classmates.Calculate your personal 'hang time,' the time your feet are off the ground during a vertical jump.How does a vector quantity differ from a scalar quantity?Why is speed classified as a scalar quantity and velocity classified as a vector quantity?If a vector that is 1 cm long represents a velocity of 10 km/h, what velocity does a vector 2 cm long drawn to the same scale represent?When a rectangle is constructed in order to add perpendicular velocities, what part of the rectangle represents the resultant vector?Will a vector at 45 to the horizontal be larger or smaller than its horizontal and vertical components? By how much?Why does a bowling ball move without acceleration when it rolls along a bowling alley?In the absence of air resistance, why does the horizontal component of velocity for a projectile remain constant while the vertical component changes?How does the downward component of the motion of a projectile compare with the motion of free fall?At the instant a ball is thrown horizontally over a level range, a ball held at the side of the first is released and drops to the ground. If air resistance is neglected, which ball strikes the ground first?a. How far below an initial straight-line path will a projectile fall in one second? b. Does your answer depend on the angle of launch or on the initial speed of the projectile? Defend your answer.Neglecting air resistance, if you throw a ball straight up with a speed of 20 m/s, how fast will it be moving when you catch it?a. Neglecting air resistance, if you throw a baseball at 20 m/s to your friend who is on first base, will the catching speed be greater than, equal to, or less than 20 m/s? b. Does the speed change if air resistance is a factor?What do we call a projectile that continually 'falls' around Earth?The vectors represent initial velocities of projectiles launched at ground level. a. Rank them by their vertical components of velocity from greatest to least. b. Rank them by their horizontal components of velocity from greatest to least.A toy car rolls off tables of various heights at different speeds as shown. a. Rank them for the time in the air, from greatest to least. b. Rank them for horizontal range, from greatest to least.Water balloons of different masses are launched by slingshots at different launching velocities v. All have the same vertical component of launching velocities. a. Rank by the time in the air, from longest to shortest. b. Rank by the maximum height reached, from highest to lowest. c. Rank by the maximum range, from greatest to least.The airplane is blown off course by wind in the directions shown. Use the parallelogram rule and rank from highest to lowest the resulting speed across the ground.For Questions 18—19, recall that when two vectors in the same or exactly opposite directions are added, the magnitude of their resultant is the sum or difference of their original magnitudes. Calculate the resultant velocity of an air-plane that normally flies at 200 km/h if it encounters a 50-km/h tailwind. If it encounters a 50-km/h headwind.For Questions 18—19, recall that when two vectors in the same or exactly opposite directions are added, the magnitude of their resultant is the sum or difference of their original magnitudes. Calculate the magnitude of the resultant of a pair of 100-km/h velocity vectors that are at right angles to each other.For Questions 20—21, recall that the resultant V of two vectors A and B at right angles to each other is found using the Pythagorean theorem: V=A2+B2 Calculate the resulting speed of an airplane with an airspeed of 120 km/h pointing due north when it encounters a wind of 90 km/h directed from the west. (Recall, speed is the magnitude of velocity.)For Questions 20—21, recall that the resultant V of two vectors A and B at right angles to each other is found using the Pythagorean theorem: V=A2+B2 Calculate the speed of raindrops hitting your face when they fall vertically at 3 m/s while you're running horizontally at 4 m/s.Whenever you add 3 and 4, the result is 7. This is true if the quantities being added are scalar quantities. If 3 and 4 are the magnitudes of vector quantities, when will the magnitude of their sum be 5?Christopher can paddle a canoe in still water at 8 km/h. How successful will he be at canoeing upstream in a river that flows at 8 km/h?How does the vertical distance a projectile falls below an otherwise straight-line path compare with the vertical distance it would fall from rest in the same time?The speed of falling rain is the same 10 m above ground as it is just before it hits the ground. What does this tell you about whether or not the rain encounters air resistance?Marshall says that when a pair of vectors are at right angles to each other, the magnitude of their resultant is greater than the magnitude of either vector alone. Renee says he is speaking in generalities and that what he says isnt always true. With whom do you agree?How is the horizontal component of velocity for a projectile affected by the vertical component?Rain falling vertically will make vertical streaks on a cars side window. However, if the car is moving, the streaks are slanted. If the streaks from a vertically falling rain make 45 streaks, how fast is the car moving compared with the speed of the falling rain?An airplane encounters a wind that blows in a perpendicular direction to the direction its nose is pointing. Does the effect of this wind increase or decrease speed across the ground below? Or does it have no effect on ground speed?A projectile is launched vertically at 50 m/s. If air resistance can be neglected, at what speed will it return to its initial level? Where in its trajectory will it have minimum speed?A batted baseball follows a parabolic path on a day when the sun is directly overhead. How does the speed of the balls shadow across the field compare with the balls horizontal component of velocity?When air resistance acts on a projectile, does it affect the horizontal component of velocity, the vertical component of velocity, or both? Defend your answer.What produces acceleration?In Chapter 4 we defined acceleration as the time rate of change of velocity. What other equation for acceleration is given in this chapter?Is acceleration directly proportional to mass, or is it inversely proportional to mass?If two quantities are inversely proportional to each other, does that mean as one increases the other increases also?If the net force acting on a sliding block is tripled, what happens to the acceleration?If the mass of a sliding block is tripled at the same time the net force on it is tripled, how does the resulting acceleration compare with the original acceleration?Motion is affected by solid objects in contact. In what other situations does friction affect motion?Suppose you exert a horizontal push on a crate that rests on a level floor, and it doesnt move. How much friction acts compared with your push?How great is the air resistance that acts on a 10-N sack that falls in air at constant velocity?Distinguish between force and pressure.When do you produce more pressure on the ground, standing or lying down?Why is it important that many nails are in the boards of Figure 6.7?What is meant by freefall?The ratio of circumference/diameter for all circles is . What is the ratio of force/mass for all freely-falling bodies?Why doesnt a heavy object accelerate more than a light object when both are freely falling?Does air resistance on a falling object increase or does it decrease with increasing speed?If two objects of the same size fall through air at different speeds, which encounters the greater air resistance?What is the acceleration of a falling object that has reached its terminal velocity?What, besides speed, affects the air resistance on a skydiver?How much air resistance acts on a falling 100-N box of nails when it reaches terminal velocity?Each diagram shows a ball traveling from left to right. The position of the ball each second is indicated by the second. Rank the net forces from greatest to least required to produce the motion indicated in each diagram. Right is positive and left is negative.Boxes of various masses are on a friction-free level table. Rank each of the following from greatest to least. a. the net forces on the boxes b. the accelerations of the boxesEach block on the friction-free lab bench is connected by a string and pulled by a second falling block. Rank each of the following from greatest to least. a. the acceleration of the two-block systems b. the tension in the strings24ACalculate the acceleration of a 40-kg crate of softball gear when pulled sideways with net force of 200 N.Calculate the acceleration of a 2000-kg, single-engine airplane as it begins its takeoff with an engine thrust of 500 N.Calculate the acceleration of a 300,000-kg jumbo jet just before takeoff when the thrust for each of its four engines is 30,000 N.Calculate the acceleration if you push with a 20-N horizontal force against a 2-kg block on a horizontal friction-free air table. F=maCalculate the horizontal force that must be applied to a 1-kg puck to make it accelerate on a horizontal friction-free air table with the same acceleration it would have if it were dropped and fell freely.Calculate the horizontal force that must be applied to produce an acceleration of 1.8g for a 1.2-kg puck on a horizontal friction-free air table.If you push horizontally on your book with a force of 1 N to make the book slide at constant velocity, how much is the force of friction on the bookTerry says that if an object has no acceleration, then no forces are exerted on it. Sherry doesnt agree, but cant provide an explanation. They both look to you. What do you say?When a car is moving in reverse, backing from a driveway, the driver applies the brakes. In what direction is the cars acceleration?The auto in the sketch moves forward as the brakes are applied. A bystander says that during the interval of braking, the autos velocity and acceleration are in opposite directions. Do you agree or disagree?What is the difference between saying that one quantity is proportional to another and saying it is equal to another?What is the acceleration of a rock at the top of its trajectory when thrown straight upward? Explain whether or not the answer is zero by using the equation a=F/m as a guide to your thinking.When blocking in football, why does a defending lineman often attempt to get his body under that of his opponent and push upward? What effect does this have on the friction force between the opposing line-mans feet and the ground?An aircraft gains speed during takeoff due to the constant thrust of its engines. When is the acceleration during takeoff greatest—at the beginning of the run along the runway or just before the aircraft lifts into the air? Think, then explain.A rocket becomes progressively easier to accelerate as it travels through outer space. Why is this so? (Hint: About 90 percent of the mass of a newly launched rocket is fuel.)A common saying goes, 'Its not the fall that hurts you; its the sudden stop.' Translate this into Newtons laws of motion.On which of these hills does the ball roll down with increasing speed and decreasing acceleration along the path? (Use this example if you wish to explain to someone the difference between speed and acceleration.)Why does a sharp knife cut better than a dull knife?When Helen lifts one foot and remains standing on a bathroom scale, pressure on the scale is doubled. Does the weight reading change?Aristotle claimed the speed of a falling object depends on its weight. We now know that objects in free fall, whatever their weights, gain speed at the same rate. Why does weight not affect acceleration?After learning why objects of different mass have the same acceleration in free fall, Erik wonders if objects tied to equal lengths of string would swing together in unison. Lisa wonders if objects of different masses would slide at equal speeds down a friction-free inclined plane. What is your thinking on these hypotheses?In a vacuum, a coin and a feather fall side by side. Would it be correct to say that in a vacuum equal forces of gravity act on both the coin and the feather?As a sky diver falls faster and faster through the air (before reaching terminal speed), does the net force on her increase, decrease, or remain unchanged? Does her acceleration increase, decrease, or remain unchanged? Defend your answers.After she jumps, a sky diver reaches terminal speed after 10 seconds. Does she gain more speed during the first second of fall or the ninth second of fall? Compared with the first second of fall, does she fall a greater or a lesser distance during the ninth second?Can you think of a reason why the acceleration of an object thrown downward through the air would actually be less than 10m/s2?How does the weight of a falling body compare with the air resistance it encounters just before it reaches terminal velocity? Just after it reaches terminal velocity?Why does a cat that falls from a 50-story building hit the safety net with no more speed than if it fell from the 20th story?A regular tennis ball and another one filled with sand are dropped at the same time from the top of a high building. Your friend says that even though air resistance is present, both balls should hit the ground at the same time because they are the same size and pass through the same amount of air. What do you say?If you drop an object, its acceleration toward the ground is 10m/s2. If you throw it downward instead, will its acceleration after throwing be greater than 10m/s2? Why or why not? (Ignore air resistance.)Suzy Skydiver, who has mass m, steps from the basket of a high-flying balloon of mass M and does a sky dive. a. What is the net force on Suzy at the moment she steps from the basket? b. What is the net force on her when air resistance builds up to equal half her weight? c. What is the net force on her when she reaches terminal speed v? d. What is the net force on her after she opens her parachute and reaches a new terminal speed 0.1 v?What is the acceleration during takeoff of a jumbo jet with a mass of 30,000 kg when the thrust for each of its four engines is 30,000 N?A net force on a 2-kg cart accelerates the cart at 3m/s2. How much acceleration will the same net force produce on a 4-kg cart?A net force of 10.0 N is exerted by Irene on a 6.7-kg cart for 3.0 seconds. Show that the cart will have an acceleration of 1.5m/s2.Toby Toobad, who has a mass of 100 kg, is skateboarding at 9.0 m/s when he smacks into a brick wall and comes to a dead stop in 0.2 s. Show that his deceleration is 45m/s2 (thats 4.5 times g—ouch!).A net force of 10.0 N on a box of plastic foam causes it to accelerate at 2.0m/s2. Show that the mass of the box is 5.0 kg.Austins truck has a mass of 2000 kg. When traveling at 22.0 m/s, it brakes to a stop in 4.0 s. Show that the magnitude of the braking force acting on the truck is 11,000 N.If a loaded truck that can accelerate at 1m/s2 loses its load and has three-fourths of its original mass, what acceleration can it attain if the same driving force acts on it?An occupant of a car can survive a crash if the deceleration during the crash is less than 30g. Calculate the force on a 70-kg person decelerating at this rate.What is the pressure on a table when a 20-N book with a 0.05-m2 cover lies flat on it? What is the pressure when the book stands on its end (area 0.01m2 )?A falling 50-kg parachutist experiences an upward acceleration of 6.2m/s2 when she opens her parachute. Show that the drag force is 810 N when this occurs.A 10-kg mass on a horizontal friction-free air track is accelerated by a string attached to another 10-kg mass hanging vertically from a pulley as shown. What is the force due to gravity, in newtons, on the hanging 10-kg mass? What is the acceleration of the system of both masses?Suppose the masses described in problem 65 are 1 kg and 100 kg, respectively. Compare the accelerations when they are interchanged, that is, for the case where the 1-kg mass dangles over the pulley, and then for the case where the 100-kg mass dangles over the pulley. What does this indicate about the maximum acceleration of such a system of masses?Skelly the skater is propelled by rocket power. Skelly and the rocket together have a mass of 25 kg. The thrusting force is 100 N and friction is 20 N. a. What is Skellys acceleration? b. How far does he go in 5 s if he starts from rest?Drop a sheet of paper and a coin at the same time. Which reaches the ground first? Why? Now crumple the paper into a small, tight wad and again drop it with the coin. Explain the difference observed. Will the coin and paper fall together if dropped from a second-, third-, or fourth-story window? Try it and explain your observations.Glue a penny to a string. When in a moving automobile, hang the string and penny out a window. Tt will be swept backward due to air resistance. When the string makes an angle of 45, easily seen with a protractor, the air resistance on the coin equals the weight of the coin. A look at the speedometer tells you the coins terminal speed in air! Do you see why the angle makes a difference?The net force acting on an object and the resulting acceleration are always in the same direction. You can demonstrate this with a spool. If the spool is gently pulled horizontally to the right, in which direction will it roll?Write a letter to a friend who has not yet studied physics and tell what you've learned about Galileo introducing the concepts of acceleration and inertia. Tell of how Galileo was also familiar with forces, but didnt see the connection among these three concepts. Tell how Isaac Newton did see the connection, revealed in his second law of motion. Explain with the second law why heavy and light objects in free fall gain the same speed in the same time. In this letter, its okay to use an equation or two, making it clear that you see equations as a shorthand notation of explanations.Can an action force exist without a reaction force?When a hammer exerts a force on a nail, how does this amount of force compare with that of the nail on the hammer?When you walk on a floor, what pushes you along?State Newtons third law of motion.Consider hitting a baseball with a bat. If we call the force the bat exerts against the ball the action force, identify the reaction force.If a bat hits a ball with 1000 N of force, can the ball exert less than 1000 N of force on the bat? More than 1000 N?If the world pulls you downward against your chair, what is the reaction force?When a cannon is fired, are the forces on the cannonball and on the cannon equal in magnitude? Are the accelerations of the two equal?When a cannon is fired, why do the cannon-ball and cannon have very different accelerations?Identify the force that propels a rocket.How does a helicopter get its lifting force?True or false: When a net force is exerted on a system, the system will accelerate, but when an applied force and its reaction are within a system, the system as a whole does not accelerate.When can two kicks on a soccer ball produce a net force of zero on the ball?14AReferring to Figure 7.14, how many horizontal forces are exerted on the cart? What is the horizontal net force on the cart?How many horizontal forces are exerted on the horse in Figure 7.14? What is the horizontal net force on the horse?How many horizontal forces are exerted on the horse—cart system in Figure 7.14? What is the horizontal net force on the horse—cart system?If you hit a wall with a force of 200 N, how much force does the wall exert on you?Can you physically touch another person without that person touching you with the same magnitude of force?