KE/PE/EPE Review Questions
M-K-S UNITS! If you are solving a problem and you are not working in METERS, KILOGRAMS, or
SECONDS, your answer will be wrong! Be careful!
Ug and K Practice Problems
ΔUg = mgh
K = ½ mv2
v = Δx
1 m = 3.28 ft
Δt
1. Usain Bolt set a world record in 2009 by running the 100m in 9.58 seconds. Calculate his kinetic energy if
his mass was 94.0 kg. Assume he ran with a constant speed. (5123 J)
2. Shani Davis of the United States won a speed-skating competition in Salt Lake City in 2009. He did this by
skating 1000m with an average speed of 54.2 km/h. If his mass was 84.0 kg, what was his kinetic energy?
(9520 J)
3. The fastest auto race in the United States is the Busch Classic at Daytona. In 1987, the winner’s average
speed was about 318 km/h. If the kinetic energy of the winning car was 3,800,000 J, what was the mass of
the car and its driver? (974 kg)
4. In 1995, Karine Dubouchet of France reached a speed of 225 km/h in downhill skiing. If Dubouchet’s mass
was 61.0 kg, what was her maximum kinetic energy? (119140 J)
5. In 1992, Sergei Bubka used a short pole to jump a height of 6.13 m. If the maximum potential energy
associated with Bubka was 4800 J at the top of his jump, what was his mass? (79.9 kg)
6. What is the potential energy of a barbell that has a mass of 182.5 kg if the barbell is lifted 1.7 m above the
ground? (3040 J)
7. Situated 4080 m above sea level La Paz, Bolivia is the highest capital in the world. If a car with a mass of
905 kg is driven to La Paz from a location that is 1860 m above sea level, what is the increase in its potential
energy? (1.969 x 107 J)
8. A mountain goat in Bolivia stands on an 850 m mountain overlooking a beautiful green pasture. The goat
has a mass of 42 kg. What is his/her potential energy? (3.499 x 105 J)
9. Cedar Point’s newest ride, The Gatekeeper, has a record inversion drop of 170 feet. The roller coaster train
has a mass of 5250-kg. What is the roller coaster’s potential energy at the very top of this 1st hill? (2.667 x
106 J)
10. Using the information in #9, what is the maximum kinetic energy the coaster will have? (2.667 x 106 J)
11. Using the information in #9, how fast can the roller coaster go (in m/s)? (31.87 m/s)
Pendulum Practice Problems
f = 1/T
T = 2π(L/g)1/2
1 Hz = 1/s
12. A student is working on a pendulum lab, and finds that his pendulum has a period of 2.15 seconds at a
location where g = 9.700 m/sec2. What is the length of the pendulum he is using? (1.14 m)
13. A clockbuilder builds the world’s tallest cuckoo clock with a pendulum that is 7.50 m long at a spot where g
= 9.825 m/sec2. Determine the frequency of the pendulum. (0.182 m)
14. The relative gravity on the surface of the moon as compared to standard Earth gravity is 0.16. A pendulum
which had a frequency of 4.00 Hz at sea level on Earth, would have what frequency when measured upon
the moon? (1.6 Hz)
15. A student wants to triple the period of a pendulum she is working with at sea level. If the pendulum was
originally 2.50 m long, how long must her new pendulum be, and how many times greater than the original
would that be? (22.5 m, 9 times)
16. The Terminal Tower in downtown Cleveland rises 52 stories above the ground, to a height of 216 m. A man
attaches a pendulum to the peak of the tower, and allows it to just reach the ground. What period would he
find that the pendulum has? (29.5 sec)
17. An astronaut is a team member of the first manned expedition to a new planet, and finds that it takes 8.00
seconds for a 50.0 cm pendulum to complete 25.0 complete oscillations. What does he measure the
acceleration due to gravity on this new planet to be? (193 m/s2)
Hooke’s Law and EPE Practice Problems
F = -kx
EPE = ½ kx2
18. A spring has a constant of 440 N/m. How much must this spring be compressed to store 25 J of potential
energy? (.238 m)
19. What force is necessary to stretch a spring whose spring constant is 120 N/m by 30 cm? (-36 N)
20. A spring with a spring constant of 600N/m is used on a scale for weighing fish. What is the mass of a fish
that would stretch the spring by 7.5 cm from its normal length? (4.59 kg)
21. A spring in a pogostick is compressed 12 cm when a 40 kg girl stands on the stick. What is the force
constant for the pogostick spring? (3267 N/m)
22. A 75 kg trampoline artist jumps vertically upward from the top of a platform with a speed of 5.0 m/s. How
fast is he going as he lands on the trampoline, which is 3.0 m below the platform? (9.2 m/s)
23. If the same trampoline has a spring constant of 5.2 x 104 N/m, how far does he depress it? (.35 m)
24. A 60 kg bungee jumper jumps from a bridge. She is tied to a 12 m long bungee cord and falls a 31 m.
Calculate the spring constant of the bungee cord. (30.95 N/m)
25. A vertical spring, whose constant is 900 N/m, is attached to a table and is compressed 0.150 m. What speed
can it give to a 0.300 kg ball when released? (11.62 m/s)
ENERGY TEST STUDY GUIDE
1. Work (equation)
a. Work done by gravity, friction, applied force (J)
b. Work at an angle (on a ramp)
2. Mechanical advantage and efficiency (know the difference between these two equations!)
a. Calculating force input and output (N)
b. Calculating work input and output (J)
3. Power (equation)
a. Horsepower and Watts (hp & W)
b. Calculating velocity with power equation
4. Kinetic and gravitational potential energy (equations)
a. How do they change relative to each other?
5. Hooke’s Law and elastic potential energy (equations)
a. Spring constant (k)
b. Calculating velocity/mass/etc. from EPE using KE or PE
6. Pendulums (equations)
a. Calculating period, frequency, and length of cord
7. Conservation of Energy
a. Energy can only be transferred from one form to another
b. Different kinds of energies
M-K-S UNITS! If you are solving a problem and you are not working in METERS, KILOGRAMS, or
SECONDS, your answer will be wrong! Be careful!