1. Energy is Conserved

2. Page 220 Example 7.9 Gravitational Potential Energy = mgh = mgy Elastic Potential Energy = ½ky 2 F spring = ky Kinetic Energy = ½mv 2 Friction Converts Mechanical Energy to Heat

3. Choose y = 0 at Point 1 At Point 1 PE spring = ½ky 2 = 0 PE grav = mgy = 0 Energy total = 16,000 J

4. Energy is Conserved At Point 2 v 2 = 0 KE = 0 y = −2 meters Energy converted to heat = F frict ∙ s = 17,000 ∙ 2 = 34,000 J Energy Accounting Started point 1 16,000 J From PE grav +39,200 J Lost to heat −34,000 J ---------------------------------------------------------------------------------- Available 16,000 J ½ky 2 = 21,200 J k = 2 ∙ 21,200 J / (2 m) 2 = 10,100 J / m 2 = 10,100 N/m