1. Chapter 5.2 Review

2. 1. A 2 kg ball is held 5 meters above the floor
1. A 2 kg ball is held 5 meters above the floor. What is its gravitational potential energy?

3. PEg = mgh PEg = 2 x 10 x 5 PEg = 100 J

4. 2. You build a 12,000 kg treehouse 5 meters above the ground
2. You build a 12,000 kg treehouse 5 meters above the ground. What is its gravitational potential energy?

5. PEg = mgh PEg = x 10 x 5 PEg = J

6. 3. A 20 kg cannonball is launched straight up at a speed of 20 m/s
3. A 20 kg cannonball is launched straight up at a speed of 20 m/s. What is its kinetic energy?

7. KE = ½ mv2 KE = ½ 20(20)2 KE = 4000 J

8. 4. What height would the cannonball in problem 3 have to reach to have potential energy equal to its initial kinetic energy?

9. PEg = mgh 4000 J = 20(10)h h = 20 m

10. 5. A bullet is fired at 1000 m/s. The mass of the bullet is 5 grams
5. A bullet is fired at 1000 m/s. The mass of the bullet is 5 grams. What is the kinetic energy of the bullet?

11. KE = ½ mv2 KE = ½ 0.005(1000)2 KE = 2500 J

12. 6. A spring with a spring constant of 500 N/m is stretched 20 cm
6. A spring with a spring constant of 500 N/m is stretched 20 cm. How much elastic potential energy is stored in the spring?

13. PEe = ½ kx2 PEe = ½ 500(0.20)2 PEe = 10 J

14. 7. A bungee cord has k = 1000 N/m. If it is stretched 5 meters, how much elastic potential energy is stored?

15. PEe = ½ kx2 PEe = ½ 1000(5)2 PEe = J