Work
Which action would require no work to be done on an object?
1) lifting the object from the floor to the ceiling
2) pushing the object along a horizontal floor against a frictional force
3) decreasing the speed of the object until it comes to rest
4) holding the object stationary above the ground
4) holding the object stationary above the ground
One elevator lifts a mass a given height in 10 seconds and a second elevator does the same work in 5 seconds. Compared to the power developed by the first elevator, the power developed by the second elevator is
1) one-half as great
2) twice as great
3) the same
4) four times as great
2) twice as great
A girl rides an escalator that moves her upward at constant speed. As the girl rises, how do her gravitational potential energy and kinetic energy change?
Ug increases, K remains the same
Compared to the total mechanical energy of the system at point A, the total mechanical energy of the system at point F is
1) less
2) more
3) the same
3) the same
A student compresses the spring in a pop-up toy 0.020 meter. If the spring has a spring constant of 340 newtons per meter, how much energy is being stored in the spring?
3.4 J
The work done by the force in pulling the object from A to B is
600 J
An electrical heater raises the temperature of a measured quantity of water. The water absorbs 6,000 joules of energy from the heater in 30.0 seconds. What is the minimum power supplied to the heater?
200 W
An object is dropped from rest from a certain height. Air resistance is negligible. After falling a distance d, the object’s kinetic energy is proportional to which of the following?
a. 1/ d2
b. 1/ d
c. sqrt(d)
d. d
e. d2
d. d
A force is applied to a block, causing it to accelerate along a horizontal, frictionless surface. The energy gained by the block is equal to the
(A) momentum given to the block
(C) power applied to the block
(B) impulse applied to the block
(D) work done on the block
(D) work done on the block
A cart of mass m traveling at speed v has kinetic energy KE. If the mass of the cart is doubled and its speed is halved, the kinetic energy of the cart will be
(1/2)KE
Weightlifter A lifts a 50 kg mass 1 m above the ground. Weightlifter B lifts an identical 50 kg mass 2 m above the ground. Compared to the work done by weightlifter A, the work done by weightlifter B is
a. ¼ as much
b. The same
c. Four times as much
d. ½ as much
e. Twice as much
e. Twice as much
A student weighing 700 N climbs at constant speed to the top of an 8 m vertical rope in 10 s. The average power expended by the student to overcome gravity is most nearly
560 W
As a pendulum swings from position A to position B, what happens to its total mechanical energy? [Neglect friction.]
(A) it decrease
(B) it increases
(C) it remains the same
(C) it remains the same
The diagram below shows a moving, 5 kg cart at the foot of a hill 10 m high. For the cart to reach the top of the hill, what is the minimum kinetic energy of the cart in the position shown? Neglect energy loss due to friction.
500 J
A 20.-newton block falls freely from rest from a point 3.0 meters above the surface of the Earth. With respect to the surface of the Earth, what is the gravitational potential energy of the block-Earth system after the block has fallen 1.5 meters?
30 J
The work done against gravity in moving the object from point A to point B is approximately
500 J
A 40.-kilogram student runs up a staircase to a floor that is 5.0 meters higher than her starting point in 7.0 seconds. The student’s power output is
280.3 W
A student compresses the spring in a pop-up toy 0.020 meter. If the spring has a spring constant of 340 newtons per meter, how much energy is being stored in the spring?
0.068 J
The diagram represents a 2 kg mass placed on a frictionless track at point A and released from rest. Assume the gravitational potential energy of the system to be zero at point E.
If the kinetic energy of the mass at point B is KB, the kinetic energy of the mass at point E is
2KB
A class of students is challenged to verify the Law of Conservation of Energy by transforming initial gravitational potential energy into kinetic energy. The students have available to them the following: Frictionless Cart Meterstick String Masses Adjustable Incline Dense Sphere Stopwatch Mass Hanger There are several methods the students could use to complete the task. However, regardless of the method each student chooses, each student will at least need.
a. Masses and a meterstick
b. Masses and a stopwatch
c. Masses and a mass hanger
d. A meterstick and a stopwatch
a. Masses and a meterstick
In the diagram below, 55 joules of work is needed to raise a 10.-newton weight 5.0 meters. How much work is done to overcome friction as the weight is raised?
5 J
The diagram below shows a 1.0 × 103 -Newton crate to be lifted at constant speed from the ground to a loading dock 1.5 meters high in 5.0 seconds. What power is required to lift the crate?
300 W
A roller coaster car of mass m = 200 kg is released from rest at the top of a 60 m high hill (position A), and rolls with negligible friction down the hill, through a circular loop of radius 20 m (positions B, C, and D), and along a horizontal track (to position E.
What is the velocity of the car at position B?
34.3 m/s
If the mass were released from rest at point B, its speed at point C would be
200 J
A block of wood, initially moving along a rough surface, is pushed with an applied horizontal force Fapplied that is less than the friction force Ffriction. Which of the following statements is false?
a. The Work being done by the applied force is negative.
b. The net Work being done on the block is negative.
c. The block is slowing down.
d. The net Work being done on the box decreases its kinetic energy K.
e. There is an increase in internal energy due to friction
a. The Work being done by the applied force is negative.