## Thursday, 11 September 2014

### KINETIC AND POTENTIAL ENERGY PROBLEMS

Determine whether the objects in the following problems have kinetic or potential energy.
Then choose the correct formula to use:            KE = 1/2 m v2                OR PE = mgh = Fwh

1. You serve a volleyball with a mass of 2.1 kg. The ball leaves your hand with a speed of 30 m/s.
The ball has ____________ energy. Calculate it.

2. A baby carriage is sitting at the top of a hill that is 21 m high. The carriage with the baby weighs
12 N. The carriage has ____________ energy. Calculate it.

3. A car is traveling with a velocity of 40 m/s and has a mass of 1120 kg. The car has ___________energy. Calculate it.

4. A cinder block is sitting on a platform 20 m high. It weighs 79 N. The block has _____________ energy. Calculate it.

5. There is a bell at the top of a tower that is 45 m high. The bell weighs 190 N. The bell has ____________ energy. Calculate it.

6. A roller coaster is at the top of a 72 m hill and weighs 966 N. The coaster (at this moment) has ____________ energy. Calculate it.

7. What is the kinetic energy of a 3-kilogram ball that is rolling at 2 meters per second?

8. The potential energy of an apple is 6.00 joules. The apple is 3.00-meters high. What is the mass of the apple?

9. Two objects were lifted by a machine. One object had a mass of 2 kilograms, and was lifted at a speed of 2 m/sec. The other had a mass of 4 kilograms and was lifted at a rate of 3 m/sec.
a. Which object had more kinetic energy while it was being lifted?

b. Which object had more potential energy when it was lifted to a distance of 10 meters? Show your
calculation.

10. You are on roller blades on top of a small hill. Your potential energy is equal to 1,000.0 joules. The last time
you checked your mass was 60.0 kilograms.
a. What is your weight in newtons?

b. If you start skating down this hill, your potential energy will be converted to kinetic energy. At the
bottom of the hill, your kinetic energy will be equal to your potential energy at the top. What will be
your speed at the bottom of the hill?

11. Answer the following:
a. What is the kinetic energy of a 1-kilogram ball is thrown into the air with an initial velocity of 30 m/sec?

b. How high into the air did the ball travel? **KE=PE

12. What is the potential energy of a 3 kilogram-ball that is on the ground?

13. What is the kinetic energy of a 2,000-kilogram boat moving at 5 m/sec?

14. What is the velocity of a 500-kilogram elevator that has 4,000 joules of energy?

15. What is the mass of an object that creates 33,750 joules of energy by traveling at 30 m/sec?

16. In a lab investigation, one group of students (group A) measures the speed of a 0.1-kilogram car at 2.5
m/secat the bottom of a hill. Another group of students (group B) measures the speed of the car at 3
m/sec at the bottom of the hill. The car’s starting position at the top of the hill is one-meter high.

a. What is the potential energy of the car at the beginning of the experiment before its speed is
measured?

b. Calculate the kinetic energy of the car for group A using the speed (2.5 m/sec) and mass values above.

c. Calculate the kinetic energy of the car for group B using the speed (3.0 m/sec) and mass values above.