Download Date ______ Period _____ CP Physics PRACTICE Quiz Work

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Date ____________ Period _____
CP Physics PRACTICE Quiz
Work, Energy, and the Work-Energy Theorem
Directions: Answer each of the following problems to the best of your ability. In all cases,
SHOW YOUR WORK, including any equation(s) you use. Make sure that your calculator is in
DEGREE MODE, and include proper units with your answer.
In order to clear his driveway of 18+ inches of snow from a recent storm, disgruntled Mr.
Bradshaw pushed down on his shovel with a force of 400 N at an angle of 35 degrees. Assume
the snow in question has a mass of 20 kg. If he pushed the snow horizontally a distance of 1.40
meters, how much work was done on the snow by…
a) the Force of Gravity?
0 J, because the force is perpendicular to the displacement.
b) the Normal Force?
0 J, because the force is perpendicular to the displacement.
c) Mr. Bradshaw’s pushing force?
W = FxCosθ = 400(1.4)Cos35 = 458.7 J
During a test drive, a driver accelerates a 2,000 kg car from a speed of 10 m/s to a speed of 20
m/s. What is the change in kinetic energy of the car? [5]
ΔKE = 1/2 mvf2 - 1/2 mv02 = 1/2(2000)(202) - 1/2(2000)(102) = 300,000 J
Intergalactic Space Superhero Ace Daring is moving some crates of space junk around the cargo
hold of his highly-experimental interstellar hyperdrive turbo-boosted rocket ship. He pushes a
100 kg crate with a horizontal force of 500 N to the right over a distance of 1.0 m to the right,
causing it to accelerate from rest to a speed of 2 m/s. Friction may or may not be acting on the
crate.
a) How much work is done by Ace Daring’s Force?
W = FxCosθ = 500(1)Cos0 = 500 J
b) What is the change in kinetic energy of the crate?
ΔKE = 1/2 mvf2 - 1/2 mv02 = 1/2(100)(22) - 0 = 200 J
c) What is the total work done to the crate?
WTotal = ΔKE = 200 J
d) The answer to (a) and (c) are different. What does this imply?
This implies that there must be a frictional force that does work (-300 J) to the box.
CP Physics PRACTICE Quiz
Work, KE, W-E Theorem
Bradshaw 2012
Name _____________________________________
Date ____________ Period _____
A dynamics cart has a mass of 1.00 kg and is accelerated from an initial velocity of 2.0 m/s to a
final velocity of 4.0 m/s. This is achieved over a distance of 1.25 m.
a) What is the change in kinetic energy of the dynamics cart?
ΔKE = 1/2 mvf2 - 1/2 mv02 = 1/2(1.00)(42) - 1/2(1.00)(22) = 6 J
b) Assuming that the force causing the car is in the exact same direction as its motion, what
is the amount of force required to accelerate the car?
WTotal = ΔKE
FxCosθ = 6
F(1.25)Cos 0 = 6
F = 4.8 N
How much work is done by the frictional force in stopping a sliding hockey puck? Assume the
mass of the hockey puck is 0.6 kg, and that it is initially sliding with a speed of 10 m/s.
WTotal = ΔKE = 1/2 mvf2 - 1/2 mv02 = 1/2(0.6)(02) - 1/2(0.6)(102) = -30 J
Multiple Choice:
Which of the following objects has the greatest kinetic energy?
a) M = 1 kg, v = 16 m/s b) M = 2 kg, v = 8 m/s c) M = 4 kg, v = 4 m/s
Choice (a) has the most; if you calculate each one, (a) is the greatest
d) M = 8 kg, v = 2 m/s
An object of mass m is initially moving with a speed v. If this speed is doubled, its kinetic energy
is increased by a factor of
a) no increase
b) 2
c) 4
d) 6
2
Choice (c) is correct; because KE depends on v , so when you double v, you are actually
doubling KE twice
In the diagram above, a force F is exerted by a broom handle on the head of the broom, which
has a mass M. The handle is at an angle θ to the horizontal, as shown above. The work done by
the force on the head of the broom as it moves a distance x across a horizontal floor is
a) Fx Cos θ
b) Fm Cos θ
c) Mx Cos θ
d) Fx Sin θ
Choice (a); By the definition of Work, W = FxCosθ
CP Physics PRACTICE Quiz
Work, KE, W-E Theorem
Bradshaw 2012