1. Science Starter! How much money could a 55 kg boy earn generating energy for the electric company if he can climb a 6.0 m tall flight of stairs in 4.0 s, and spends 10 hours climbing stairs at this rate? (The electric company charges $0.11 per kWh)

2. Work – Energy Theorem

3. Kinetic Energy

4. A 5 kg dog is surfing, traveling at a speed of 2 m/s. How much kinetic energy does the dog possess? K = ½ mv 2 m = 5 kg v = 2 m/s K = ? K = ½ mv 2 K = ½ (5)(2) 2 K = 10 J

5. Gravitational Potential Energy

6. A 70 kg bungee jumper is about to take the plunge from a 100 m tall crane. How much gravitational potential energy does the jumper possess? U g = mgh m: 70 kg g: 9.8 m/s 2 h: 100 m U g = ? U g = mgh U g = (70)(9.8)(100) U g = 68600 J

8. A boy is shooting a rock using a sling shot that has a spring constant of 5 N/m. He pulls the string back 10 cm. How much elastic potential energy is stored in the slingshot? U e = ½ kx 2 k = 5 N/m x = 0.1 m U e = ? U e = ½ kx 2 U e = ½ (5)(.10) 2 U e = 0.025 J

9. Total Energy

10. Work – Energy Theorem Example: A 20 kg bike traveling at 4 m/s coasts through a patch of dirt, slowing down to 1 m/s. (a) How much work was done on the bike by the dirt in slowing it down? (b) How much force was exerted on the bike if the dirt stretched for 3 m?