A 33.0 kg child slides down a long slide in a play ground. she starts from rest at a height h1 of 19.00 m. When she is partway down the slide, at a height h2 of 9.00 m, she is moving at a speed of 8.90 m/s. Calculate the mechanical energy lost due to friction. I know that Conservation of mechanical energy is K2 + U2 = K1 + U1. I don't really know how to start this problem though. Any help would be appreciated.