d. A 9.2 Work and Kinetic Energy for a Single Particle 2 On the axes below, draw graphs of the kinetic energy of a. A 1000 kg car that uniformly accelerates from 0 to 20 m/s in 20 s. b. A 1000 kg car moving at 20 m/s that brakes to a halt with uniform deceleration in 20 s. c. A 1000 kg car that drives once around a 130-m-diameter circle at a speed of 20 m/s. Calculate K at several times, plot the points, and draw a smooth curve between them. K (J) b. K (J) с. K (J) a. 250,000 250,000 250,000 200,000 200,000 200,000 150,000 150,000 150,000 100,000 100,000 100,000 50,000 50,000 50,000 - t(s) - 1(s) 0+ 0 5 10 15 20 t (s) 04 O 5 04 0 5 10 15 20 10 15 20 Exercises 3-10: For each situation: Draw a before- and-after pictorial representation. .Draw and label the displacement vector Ar. Draw a free-body diagram. . Fill in the table by showing the sign (+, -, or 0) of the quantities listed. 3. An elevator moves up at constant speed. ten W grav

d. A 9.2 Work and Kinetic Energy for a Single Particle 2 On the axes below, draw graphs of the kinetic energy of a. A 1000 kg car that uniformly accelerates from 0 to 20 m/s in 20 s. b. A 1000 kg car moving at 20 m/s that brakes to a halt with uniform deceleration in 20 s. c. A 1000 kg car that drives once around a 130-m-diameter circle at a speed of 20 m/s. Calculate K at several times, plot the points, and draw a smooth curve between them. K (J) b. K (J) с. K (J) a. 250,000 250,000 250,000 200,000 200,000 200,000 150,000 150,000 150,000 100,000 100,000 100,000 50,000 50,000 50,000 - t(s) - 1(s) 0+ 0 5 10 15 20 t (s) 04 O 5 04 0 5 10 15 20 10 15 20 Exercises 3-10: For each situation: Draw a before- and-after pictorial representation. .Draw and label the displacement vector Ar. Draw a free-body diagram. . Fill in the table by showing the sign (+, -, or 0) of the quantities listed. 3. An elevator moves up at constant speed. ten W grav

Physics for Scientists and Engineers with Modern Physics

10th Edition

ISBN:9781337553292

Author:Raymond A. Serway, John W. Jewett

Publisher:Raymond A. Serway, John W. Jewett

Chapter7: Energy Of A System

Section: Chapter Questions

Problem 25P: Review. You can think of the workkinetic energy theorem as a second theory of motion, parallel to...

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. A bicycle and rider going 10 m/s approach a hill. Their total mass is 80 kg. (a) What is their kinetic energy? (b) If the rider coasts up the hill without pedaling, how high above its starting level will the bicycle be when it finally rolls to a stop?
A running 62-kg cheetah has a top speed of 32 m/s. (a) What is the cheetahs maximum kinetic energy? (b) Kind the cheetahs speed when its kinetic energy is one half of the value found in part (a).
A 60.0-kg athlete leaps straight up into the air from a trampoline with an initial speed of 9.0 m/s. The goal of this problem is to find the maximum height she attains and her speed at half maximum height. (a) What are the interacting objects and how do they interact? (b) Select the height at which the athletes speed is 9.0 m/s as y = 0. What is her kinetic energy at this point? What is the gravitational potential energy associated with the athlete? (c) What is her kinetic energy at maximum height? What is the gravitational potential energy associated with the athlete? (d) Write a general equation for energy conservation in this case and solve for the maximum height. Substitute and obtain a numerical answer. (e) Write the general equation for energy conservation and solve for the velocity at half the maximum height. Substitute and obtain a numerical answer.
Suppose a 350-g kookaburra (a large kingfisher bird) picks up a 75-g snake and raises it 2.5 m from the ground to a branch. (a) How much work did the bird do on the snake? (b) How much work did it do to raise its own center of mass to the branch?
Integrated Concepts (a) What force must be supplied by an elevator cable to produce an acceleration of 0.800 m/s2 against a 200-N frictional force, if the mass of the loaded elevator is 1500 kg? (b) How much work is done by the cable in lifting the elevator 20.0 m? (c) What is the final speed of the elevator if it starts from rest? (d) How much work went into thermal energy?
Review. You can think of the workkinetic energy theorem as a second theory of motion, parallel to Newtons laws in describing how outside influences affect the motion of an object. In this problem, solve parts (a), (b), and (c) separately from parts (d) and (e) so you can compare the predictions of the two theories. A 15.0-g bullet is accelerated from rest to a speed of 780 m/s in a rifle barrel of length 72.0 cm. (a) Find the kinetic energy of the bullet as it leaves the barrel. (b) Use the workkinetic energy theorem to find the net work that is done on the bullet. (c) Use your result to part (b) to find the magnitude of the average net force that acted on the bullet while it was in the barrel. (d) Now model the bullet as a particle under constant acceleration. Find the constant acceleration of a bullet that starts from rest and gains a speed of 780 m/s over a distance of 72.0 cm. (e) Modeling the bullet as a particle under a net force, find the net force that acted on it during its acceleration. (f) What conclusion can you draw from comparing your results of parts (c) and (e)?
A 3.00-kg object has a velocity (6.00i1.00j)m/s. (a) What is its kinetic energy at this moment? (b) What is the net work done on the object if its velocity changes to (8.00i+4.00j)m/s. (Note: From the definition of the dot product, v2=vv.)
Two children stand on a platform at the top of a curving slide next to a backyard swimming pool. At the same moment the smaller child hops off to jump straight down into the pool, the bigger child releases herself at the top of the frictionless slide. (i) Upon reaching the water, the kinetic energy of the smaller child com-pared with that of the larger child is (a) greater (b) less (c) equal. (ii) Upon reaching the water, the speed of the smaller child compared with that of the larger child is (a) greater (b) less (c) equal. (iii) During their motions from the platform to the water, the average acceleration of the smaller child compared with that of the larger child is (a) greater (b) less (c) equal.
One person drops a ball from the top of a building while another person at the bottom observes its motion. Will these two people agree (a) on the value of the gravitational potential energy of the ballEarth system? (b) On the change in potential energy? (c) On the kinetic energy of the ball at some point in its motion?
A 60.0-kg athlete leaps straight up into the air from a trampoline with an initial speed of 9.0 m/s. The goal of this problem is to find the maximum height she attains and her speed at half maximum height. (a) What are the interacting objects and how do they interact? (b) Select the height at which the athletes speed is 9.0 m/s as y = 0. What is her kinetic energy at this point? What is the gravitational potential energy associated with the athlete? (c) What is her kinetic energy at maximum height? What is the gravitational potential energy associated with the athlete? (d) Write a general equation for energy conservation in this case and solve for the maximum height. Substitute and obtain a numerical answer. (e) Write the general equation for energy conservation and solve for the velocity at half the maximum height. Substitute and obtain a numerical answer.
The launching mechanism of a toy gun consists of a spring of unknown spring constant, as shown in Figure P5.39a. If the spring is compressed a distance of 0.120 m and the gun fired vertically as shown, the gun can launch a 20.0-g projectile from rest to a maximum height of 20.0 m above the starting point of the projectile. Neglecting all resistive forces, (a) describe the mechanical energy transformations that occur from the time the gun is fired until the projectile reaches its maximum height, (b) determine the spring constant, and (c) find the speed of the projectile as it moves through the equilibrium position of the spring (where x = 0), as shown in Figure P5.39b. Figure P5.39