Work, Energy, and Power

A 1000-kg car is moving at 40.0 km/hr when the driver slams on the brakes and skids to a stop (with locked brakes) over a distance of 20.0 meters. How far will the car skid with locked brakes if it is traveling at 120. km/hr? (Displacement will be equal to 3^2) a. 20.0 m b. 60.0 m c. 90.0 m d. 120. m e. 180. m

e. 180. m

An acorn falls from a tree. During the fall, compare its kinetic energy K, to its potential energy U. A. K increases and U decreases. B. K decreases and U decreases. C. K increases and U increases. D. K decreases and U increases.

A. K increases and U decreases.

A baseball and a ping pong ball are both shot from a slingshot with equal velocity. Which ball has the greater kinetic energy? A. the baseball B. the ping pong ball C. the answer depends on the lunch angle D. the kinetic energies are equal

A. the baseball

A 50- kg platform diver hits the water below with a kinetic energy of 5000 Joules. The height (relative to the water) from which the diver dove was approximately ___ meters. A. 5 B. 10 C. 50 D. 100

B. 10

A horizontal force of 200 N is applied to move a 55-kg cart (initially at rest) across a 10 m level surface. What is the final kinetic energy of the cart? (KE = Force*distance) A. 1.0 × 10^3 J B. 2.0 × 10^3 J C. 2.7 × 10^3 J D. 4.0 × 10^3 J

B. 2.0 × 10^3 J

A 15.0-kg object is moved from a height of 7.00 m above a floor to a height of 13.0 m above the floor. What is the change in gravitational potential energy? (Change in gravitational potential energy = mghf - mghi) A. zero B. 1030 J C. 1176 J D. 1910 J

C. 1176 J

A ball falls from the top of a building, through the air (air friction is present), to the ground below. How does the kinetic energy (K) just before striking the ground compare to the potential energy (U) at the top of the building? A. K is equal to U. B. K is greater than U. C. K is less than U. D. It is impossible to tell.

C. K is less than U.

A 10-kg mass is moving with a speed of 5.0 m/s. How much work is required to stop the mass? (KE = Work Done) (KE = 1/2mv^2) A. 50 J B. 75 J C. 100 J D. 125 J

D. 125 J

A 10-Newton object moves to the left at 1 m/s. Its kinetic energy is approximately ___ Joules. a. 0.5 b. 1 c. 10 d. more than 10

a. 0.5

A force accelerates a 5 kg box from a speed of 2.5 m/s to a speed of 4.0 m/s in 5 s. The work done by this force over this time is (W = 1/2mvfinal^2 - 1/2mvinitial^2) a. 25 J b. 47 J c. 62.5 d. more information needed

a. 25 J

An arrow is drawn back so that 50 Joules of potential energy is stored in the stretched bow and string. When released, the arrow will have a kinetic energy of __ Joules. a. 50 b. more than 50 c. less than 50

a. 50

How much work is done on a 50-N rock that you lift 10 m straight up? (Work = Force*displacement) a. 500 J b. 50 J c. 10 J d. 1 J

a. 500 J

You push a box across the floor a distance of 5 m exerting a steady force of 150 N. If it takes 10 s to move the box, your power is (Power = (Force*distance)/time) a. 75 W b. 90 W c. 150 W d. 750 W

a. 75 W

A ball is projected into the air with 100 J of kinetic energy. The kinetic energy is transformed into gravitational potential energy on the path towards the peak of its trajectory. When the ball returns to its original height, its kinetic energy is Joules. Do consider the effects of air resistance. a. less than 100 b. 100 c. more than 100 d. not enough information given

a. less than 100

An object that has kinetic energy must be a. moving b. falling c. elevated d. at rest

a. moving

Of the following, which is not a unit of power? a. watt/second b. newton-meter/second c. joule/second d. watt

a. watt/second

The area under the curve, on a Force versus position (F vs. x) graph, represents a. work b. kinetic energy c. power d. potential energy

a. work

A child lifts a box up from the floor. The child then carries the box with constant speed to the other side of the room and puts the box down. How much work does he do on the box while walking across the floor at constant speed? a. zero J b. more than zero J c. more information needed to determine

a. zero J

Luke Autbeloe stands on the edge of a roof throws a ball downward. It strikes the ground with 100 J of kinetic energy. Luke now throws another identical ball upward with the same initial speed, and this too falls to the ground. Neglecting air resistance, the second ball hits the ground with a kinetic energy of ___ J. a. less than 100 b. 100 c. 200 d. more than 200 e. none of these

b. 100

Car J moves twice as fast as car K, and car J has half the mass of car K. The kinetic energy of car J, compared to car K is a. the same. b. 2 to 1. c. 4 to 1. d. 1 to 2.

b. 2 to 1.

A person ascends a flight of stairs in 20 s. The person weighs 500 N and the vertical height of the stairs is 9 m. The person's power output is (Power = (Force*distance)/time) a. 150 W b. 225 W c. 325 W d. 450 W

b. 225 W

If you lift a box of mass 5 kg straight up at constant speed through a displacement of 1m, the total work done on the box by gravity is (Work = Force*distance) (Force = mass*acceleration) a. Zero joules b. 49 J c. - 49 J d. 25 J

b. 49 J

Two young men of about the same weight climb the same set of stairs. One does in 10 seconds while the other does it in 12.3 seconds. Who develops more power? a. The one who climbed in 12.3 seconds b. The one who climbed in 10 seconds c. Both generate the same power d. More information is needed.

b. The one who climbed in 10 seconds

Two young men of about the same weight climb the same set of stairs. One does in 10 seconds while the other does it in 12.3 seconds. Who transfers more energy? a. The one who climbed in 12.3 seconds b. The one who climbed in 10 seconds c. Both transfer the same amount of energy d. More information is needed.

b. The one who climbed in 10 seconds

If you lift one load up two stories, how much work do you do compared to lifting one load up one story. a. Four times as much b. Twice as much c. The same amount d. one half as much

b. Twice as much

More power is needed to carry a heavy suitcase slowly up a flight of stairs than to carry the suitcase quickly up the same flight of stairs. a. true b. false c. not enough information

b. false

The quantity mgh is a. the kinetic energy of the object. b. the gravitational potential energy of the object. c. the work done on the object by the force. d. the power supplied to the object by the force.

b. the gravitational potential energy of the object.

A box of mass 5 kg is accelerated by a force across the floor at a rate of 2m/s/s for 10 s. The work done by the force is (F = ma) (displacement (d) = ut + 1/2at^2) (W = Fd) a. 50 J b. 100 J c. 1000 J d. 1500 J

c. 1000 J

During a construction proiect, a 2500 N obiect is lifted high above the ground. It is released and falls 10.0 meters and drives a post 0.100 m into the ground. The average impact force on the object is ___ Newtons. a. 2500 b. 25000 c. 250,000 d. 2,500,000

c. 250,000

Two young men of about the same weight climb the same set of stairs. One does in 10 seconds while the other does it in 12.3 seconds. Who does more work? a. The one who climbed in 12.3 seconds b. The one who climbed in 10 seconds c. Both do the same amount of work d. More information is needed.

c. Both do the same amount of work

A box is dragged across a floor by a force F which makes an angle of O with the horizontal. As O is increased with the magnitude of F held constant the work done by F a. remains the same b. increases c. decreases d. increases then decreases

c. decreases

If the net work done on an object is positive, then the object's kinetic energy a. decreases b. remains the same. c. increases. d. is zero.

c. increases

The angle between a force F and a displacement d is 125 degrees. The work done by the force is a. zero b. positive c. negative d. the sign depends on the magnitudes of F and d

c. negative

A 1200 kg car and a 2400 kg car are lifted to the same height at a constant speed in an auto service station. Lifting the more massive car requires ___ work. a. less b. the same c. twice as much d. four times as much e. more than 4 times as much

c. twice as much

A platform diver weighs 500 N. She steps off a diving board that is elevated to a height of 10 meters above the water. The diver will possess ___ Joules of kinetic energy when she hits the water. a. 10 b. 500 c. 510 d. 5000 e. more than 5000

d. 5000

A truck weighs twice as much as a car, and is moving at twice the speed of the car. Which statement is true about the truck's kinetic energy compared to that of the car? a. All that can be said is that the truck has more kinetic energy. b. The truck has twice the kinetic energy of the car. c. The truck has 4 times the kinetic energy of the car. d. The truck has 8 times the kinetic energy of the car.

d. The truck has 8 times the kinetic energy of the car.

Work is done on an object when a constant force is exerted on the object causing it to be displaced _________ a. opposite the direction of the force b. at an angle to the force c. perpendicular to the force d. in the direction of the force

d. in the direction of the force

Which of the following items relates to power but not work? a. distance b. force c. mass d. time

d. time

A spring is characterized by a spring constant of 60 N/m. How much potential energy does it store, when stretched by 1.0 cm? (Convert cm to m) (PE = (0.5)spring constant*displacement^2 A. 3.0 × 10-3 J B. 0.30 J C. 60 J D. 600 J

A. 3.0 × 10-3 J

The quantity 1/2mv^2 is a. the kinetic energy of the object. b. the potential energy of the object. c. the work done on the object by the force. d. the power supplied to the object by the force.

A. the kinetic energy of the object.

Using 1000. J of work, a small object is lifted from the ground floor to the third floor of a tall building in 20.0 seconds. What power was required in this task? A. 20 W B. 50 W C. 100 W D. 1000 W E. 20000 W

B. 50 W

Which of the following would produce the greatest increase in the kinetic energy of a moving object? A. doubling its mass B. doubling its velocity C. halving its mass D. halving its velocity

B. doubling its velocity

The quantity 1/2 kx2 is A. the kinetic energy of the object. B. the elastic potential energy of the object. C. the work done on the object by the force. D. the power supplied to the object by the force.

B. the elastic potential energy of the object.

A 50.0 kg crate is lifted to a height of 2.0 meters in the same time as a 25.0 kg crate is lifted to a height of 4 meters. The rate at which energy is used (i.e., power) in raising the 50.0 kg crate is ___ as the rate at which energy is used to life the 25.0 kg crate. A. Twice as much B. Half as much C. the same

C. the same

An object at rest may have ___ A. Speed B. Velocity C. Acceleration D. Energy E. All of these

D. Energy

A job is done slowly, and an identical job is done quickly. Both jobs require the same amount of ___, but different amounts of ___. Pick the two words which fill in the blanks in their respective order. A. Energy, work B. Power, work C. Work, energy D. Work, power

D. Work, power

The total mechanical energy of a system A. is equally divided between kinetic energy and potential energy. B. is either all kinetic energy or all potential energy, at any one instant. C. can never be negative. D. is constant, only if the system is closed and isolated.

D. is constant, only if the system is closed and isolated.