# Forces and Free Body Diagrams

1. The kinetic energy of a car moving at 30km/h is 2MJ. When the car is moving at 90km/h, what is the kinetic energy?

2. A brick falls off a ledge 30 meters above the ground. An identical brick falls off another ledge 60 meters high. What can you say about the kinetic energies of the bricks, if you compare their kinetic energies just before he bricks hit the ground (ignore air resistance)?

3. For the same bricks, what can you say about the speeds of the two bricks, right before they hit the ground (ignore air resistance)?

4. When a ball, starting from rest, rolls down a hill, its speed at the bottom of the hill is 8 m/s. If instead, the ball starts with an initial velocity of 6 m/s at the top of the hill, how fast will it be going at the bottom of the same hill? Assume there are no energy losses due to friction or drag forces.

5. A 6.5kg bowling ball is dropped from a place 30 meters above the ground, and falls into a hole 20 meters deep. What is the change in the gravitational potential energy of the bowling ball?

6. Use the information about the falling bowling ball from the previous question. Assuming there are no drag forces, what is the speed of the bowling ball just before it hits the bottom of the hole?

7. Three acrobats are using a "se-saw", by having two acrobats land on the see-saw simultaneously after falling from 10 meters, while the third acrobat is standing on the other end of the see-saw. Assume all three acrobats have the same mass, and ignore friction and drag forces. How high will the third acrobat go up into the air?

8. Using the same information about the acrobats, what is the "take-off" speed of the third acrobat from the see-saw, compared to the speed of the two acrobats when they landed on the see-saw?

9. When you throw a ball at a given speed, it has a given amount of kinetic energy when it leaves your hand. In order to throw a ball so that it has three times as much kinetic energy, you must throw the ball at what speed?

10. A baseball has a mass of 167 grams. If you throw it at 12 m/s, how much work did you do on the ball?

#### Solution Summary

Solution includes formulas, full calculations and answers for each of the ten questions in the problem set.