Question

A 30.0 kg child slides down a long slide in a playground. She starts from rest at a height h1 of 18.00 m. When she is partway down the slide, at a height h2 of 9.00 m, she is moving at a speed of 9.30 m/s. Calculate the mechanical energy lost due to friction (as heat, etc.).

Answer 1

loss of potential energy = m g (18-9)
so
mg(18-9) = (1/2) m v^2 + loss due to friction
or

30(9.8)(9) = 15(9.3)^2 + loss due to friction