Concept explainers
BIO Brain Power The human brain consumes about 22 W of power under normal conditions, though more power may be required during exams. (a) For what amount of time can one Snickers bar (see the note following Problem 48) power the normally functioning brain? (b) At what rate must you lift a 3.6-kg container of milk (one gallon) if the power output of your arm is to be 22 W? (c) How much time does it take to lift the milk container through a distance of 1.0 m at this rate?
Want to see the full answer?
Check out a sample textbook solutionChapter 7 Solutions
Physics (5th Edition)
Additional Science Textbook Solutions
College Physics
Physics for Scientists and Engineers: A Strategic Approach with Modern Physics (4th Edition)
The Cosmic Perspective (8th Edition)
Cosmic Perspective Fundamentals
Glencoe Physical Science 2012 Student Edition (Glencoe Science) (McGraw-Hill Education)
The Cosmic Perspective Fundamentals (2nd Edition)
- Construct Your Own Problem Consider a person climbing and descending stairs. Construct a problem in which you calculate the long-term rate at which stairs can be climbed considering the mass of the person, his ability to generate power with his legs, and the height of a single stair step. Also consider why the same person can descend stairs at a faster rate for a nearly unlimited time in spite of the fact that very similar forces are exerted going down as going up. (This points to a fundamentally different process for descending versus climbing stairs.)arrow_forwardCalculate the power output in watts and horsepower of a shot-putter who takes 1.20 s to accelerate the 7.27-kg shot from rest to 14.0 m/s, while raising it 0.800 m. (Do not include the power produced to accelerate his body.) Figure 7.42 Shot putter at the Dornoch Highland Gathering in 2007. (credit: John Haslam, Flickr)arrow_forwardIntegrated Concepts (a) Calculate the force the woman in Figure 7.46 exerts to do a push-up at constant speed, taking all data to be known to three digits. (b) How much work does she do if her center of mass rises 0.240 m? (c) What is her useful power output if she does 25 push-ups in 1 min? (Should work done lowering her body be included? See the discussion of useful work in Work, Energy, and Power in Humans. Figure 7.46 Forces involved in doing push-ups. The woman's weight acts as a force exerted downward on her center of gravity (CG).arrow_forward
- A hummingbird is able to hover because, as the wings move downward, they exert a downward force on the air. Newtons third law tells us that the air exerts an equal and opposite force (upward) on the wings. The average of this force must be equal to the weight of the bird when it hovers. If the wings move through a distance of 3.5 cm with each stroke, and the wings beat 80 times per second, determine the work performed by the wings on the air in 1 m if the mass of the hummingbird is 3.0 g.arrow_forwardConfirm the value given for the kinetic energy of an aircraft carrier in Table 7.1. You will need to look up the definition of a nautical mile (1knot=1nauticalmile/h) .arrow_forwardTwo 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.arrow_forward
- . An archer using a simple bow exerts a force of 180 N to draw back the bow string 0.50 m. (a) What is the average work done by the archer in preparing to launch her arrow? (Hint: Compute the average work as you would any average quantity: average work = [final work - initial work].) (b) If all the work is converted into the kinetic energy of the arrow upon its release, what is the arrow's speed as it leaves the bow? Assume the mass of the arrow is 0.021 kg and ignore any kinetic energy in the bow as it relaxes to its original shape. (c) If the arrow is shot straight up, what is the maximum height achieved by the arrow? Ignore any effects due to air resistance in making your assessment.arrow_forwardThe kinetic energy of a system must always be positive or zero. Explain whether this is true for the potential energy of a system.arrow_forwardA car accelerates uniformly from rest. Ignoring air friction, when does the car require the greatest power? (a) When the car first accelerates from rest, (b) just as the car reaches its maximum speed, (c) when the car reaches half its maximum speed. (d) The question is misleading because the power required is constant. (e) More information is needed.arrow_forward
- A sprinter of mass m accelerates uniformly from rest to velocity v in t seconds. (a) Write a symbolic expression for the instantaneous mechanical power P required by the sprinter in terms of force F and velocity v. (b) Use Newtons second law and a kinematic equation for the velocity at any time to obtain an expression for the instantaneous power in terms of m, a, and t only. (c) If a 75.0-kg sprinter reaches a speed of 11.0 m/s in 5.00 s, calculate the sprinters acceleration, assuming it to be constant. (d) Calculate the 75.0-kg sprinters instantaneous mechanical power as a function of time t and (e) give the maximum rate at which he burns Calories during the sprint, assuming 25% efficiency of conversion form food energy to mechanical energy.arrow_forwardA 1 000-kg roller coaster car is initially at the top of a rise, at point . It then moves 135 ft, at an angle of 40.0 below the horizontal, to a lower point . (a) Choose the car at point to be the zero configuration for gravitational potential energy of the roller coasterEarth system. Find the potential energy of the system when the car is at points and , and the change in potential energy as the car moves between these points. (b) Repeat part (a), setting the zero configuration with the car at point .arrow_forward. A particular hydraulic pile driver uses a ram with a mass of 1040 kg. If the maximum pile energy is 11,780J, how high must the ram he raised to achieve this value? Assuming it takes 0.62 s for the pile driver’s winch motor to raise the ram at a constant speed to this height, what is the power output by the motor in completing this task? Express your answer in both watts and horsepower.arrow_forward
- College PhysicsPhysicsISBN:9781938168000Author:Paul Peter Urone, Roger HinrichsPublisher:OpenStax CollegeCollege PhysicsPhysicsISBN:9781305952300Author:Raymond A. Serway, Chris VuillePublisher:Cengage Learning
- Physics for Scientists and Engineers, Technology ...PhysicsISBN:9781305116399Author:Raymond A. Serway, John W. JewettPublisher:Cengage LearningCollege PhysicsPhysicsISBN:9781285737027Author:Raymond A. Serway, Chris VuillePublisher:Cengage LearningPhysics for Scientists and Engineers: Foundations...PhysicsISBN:9781133939146Author:Katz, Debora M.Publisher:Cengage Learning