1. Chapter 12 Work, Energy and Power

2. Energy Is the ability to do work Expressed in Joules (dzuls) Forms of energy: Mechanical, Heat, light, and Chemical Energy

3. ENERGY POTENTIAL ENERGY Gravitational potential energy Elastic potential energy KINETIC ENERGY

4. POTENTIAL ENERGY Gravitational Energy Elastic Potential Energy

5. Gravitational Potential Energy Is the energy possessed by a body by virtue of its position PE = mgh

6. Sample Problem 1 A 75.0kg child climbs a 6.00m long slide. What is the potential energy of the child? Given: m = 75.0kg, h = 6.00m, g = 9.8m/s 2 Required: PE = ? Sol’n: PE = mgh = (75kg) (6m) (9.8m/s 2 ) = 4 410 kg m 2 /s 2 = 4 410 J

7. Sample Problem 2 The potential energy of an apple is 6.00 joules. The apple is 3.00-meters high. What is the mass of the apple? Given: h = 3.00m, PE =6.00 J, g = 9.8m/s 2 Required: m = ?

8. Elastic Potential Energy Is the energy possessed by a spring or rubber band when it is stretched or compressed

9. Kinetic Energy Is the energy possessed by a body because of its motion KE = ½ mv 2

10. Sample Problem 3 What is the kinetic energy of a 2,000 kilogram boat moving at 5 m/s? Given: m = 2,000kg, v = 5m/s Required: KE = ? Sol’n:KE = ½ mv 2 = ½ (2000kg) (5m/s) 2 = 1000kg (25m 2 /s 2 ) = 25,000 J

11. Sample Problem 4 What is the velocity of an 500-kilogram elevator that has 4,000 joules of energy? Given: m = 5,000kg, KE = 4,000 J Required: v = ?

12. Sample Problem 5 What is the height of a raised object where its mass is 25kg and the potential energy is 34 J?

13. Sample Problem 6 What is the mass of an object where its velocity is 25m/s and its kinetic energy is 38.03 J?