Question

A 36 kg child slides down a slide that is 2.5m high. At the bottom of the slide she is moving at 3.0m/s. How much energy was lost as she slid down the slide?

Answer 1

$\text{At the top of the slide:} \\\\ P.E. = mgh = (36)(9.8)(2.5) = 882 \text{J} \\ K.E. = 0 \text{, because the child is not moving.} \\ \text{Total energy} = 882J \\\\ \text{At the bottom of the slide:} \\\\ P.E. = 0 \text{, because the child is on the ground.} \\ K.E. = \frac{1}{2}mv^2 = \frac{1}{2}(36)(3)^2 = (18)(9) = 162J \\ \text{Total energy} = 162J \\\\ \text{Energy lost} = 882 = 162 = 720J$