Physics 131 Test/Exam Problems: Work and Energy
1) The driver of an empty speeding truck slams on the brakes and skids to a stop in a
distance D. If the truck were carrying a load that doubled its mass, what would its
stopping distance have been? (Assume the road is straight and horizontal and that the
coefficient of kinetic friction is constant). (a)
(a) D
(b) 2D
(c) D/2
2) The change in kinetic energy of an object is always equal to the net work done on that
object by all acting forces. (T)
(T) True
(F) False
3) Two objects have the same momentum, but have different masses. If KH and KL are the
kinetic energies of the heavier and the lighter object respectively then: (a)
(a) KH < KL
(b) KH = KL
(c) KH > KL
4) A block is moved 2.5 meters across a floor by two 20 N forces. The force F1 pushes at an
angle down, and the force F2 pushes directly horizontally. Compare W the work done by
the two forces. (a)
(a) W1 < W2
(b) W1 = W2
(c) W1 > W2
5) A block of mass M = 1 kg is on a horizontal frictionless table and is attached to one end
of a taut string of length L = 0.5 m. The block is spun around in a horizontal circle with a
constant speed v = 3 m/s. A top view of the table and block is shown in the figure. The
work done on the object by the string during half a revolution is (c)
(a) 28 J
(b) 57 J
(c) zero
6) A force F is applied to block A of mass M over a distance D on a horizontal frictionless
surface. The same force F is applied to block B of mass 2M over the same distance. Both
blocks are initially at rest. Which block ends up with the larger kinetic energy? (c)
(a) Block A.
(b) Block B.
(c) Both blocks end up with the same kinetic energy.
7) An object of mass M = 5 kg is moving horizontally in a straight line at a speed of 6 m/s.
A force of 100 N is applied over a short period of time such that the speed of the object
increases to 10 m/s. (e)
The work done by the force is
(a)
(b)
(c)
(d)
(e)
100 J
15 J
5J
260 J
160 J
8) A crane does a certain amount of work to lift a load from the ground to a height of 3 m in
a time of 5 s. If it lifts it instead in 15 s, the work done would (c)
(a) increase.
(b) decrease.
(c) stay the same.
9) I pull a pail of water with mass 2 kg out of a well with a force of 20 N. If the pail starts at
rest, how much work total is done to it after I pull it up 4 m? What velocity will it have
after this time? (1.6 J, 1.26 m/s)
10) If a car of mass 500 kg is going at 50 m/s, how much work is required to stop the car?
(6.25  105 J)
11) A baseball of mass 0.140 kg traveling at 35 m/s hits a fielder’s glove and moves it back
25 cm. What was the force that the glove applied? Assume the glove applies a constant
force. (343 N)
12) At an accident scene on a level road, investigators measure a car’s skid mark to be 88 m
long. It was a rainy day and the coefficient of friction was estimated to be 0.42. Use this
data to determine the speed of the car when the brakes were applied and locked. Were
they speeding in a 55 mph zone? (26.9 m/s)
13) A toy car has a kinetic energy of 8 J. What is its kinetic energy after a dissipative force
of 0.5 N has acted on it for 6m? (5 J)