9. Skiing Example (no friction) A skier goes down a 78 meter high hill with a variety of slopes. What is the maximum speed she can obtain if she starts from rest at the top? Conservation of energy:  W nc =  K +  U K i + U i = K f + U f ½ m v i 2 + m g y i = ½ m v f 2 + m g y f 0 + g y i = ½ v f 2 + g y f v f 2 = 2 g (y i -y f ) v f = sqrt( 2 g (y i -y f )) v f = sqrt( 2 x 9.8 x 78) = 39 m/s 26 0 = K f -K i + U f - U i

14. Skiing w/ Friction A 50 kg skier goes down a 78 meter high hill with a variety of slopes. She finally stops at the bottom of the hill. If friction is the force responsible for her stopping, how much work does it do? Work Energy Theorem: W nc = K f -K i + U f - U i = ½ m v f 2 - ½ m v i 2 + m g y f – m g y i = 0+0+0 - g y i m = – 764 x 50 Joules = -38200 Joules Similar to bob sled homework