Child on Slide?

Question

A 35.0 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 6.00 m, she is moving at a speed of 8.10 m/s. Calculate the mechanical energy lost due to friction (as heat, etc.).

Answer 1

There is probably an equation you use. First what you do is list your knowns:

m = 35.0 kg
h1 = 18.00 m
h2 = 6.00 m
v = 8.10 m/s
mechanical energy = ?

Now just look for an equation with those variables.

Answer 2

She has lost 12 m of height, which means gravity has done a total of
mgh = 35*9.8*12 = 4116 J. Her speed is 8.1 m's so her kinetic energy is
mv²/2 = 35*8.1²/2 = 1148 J so the total energy lost to frictional heat, etc. is
4116 - 1148 = 2968 J


Doug