Energy Dissipation Question

Question

An object with the mass of .1 kg was dropped from a cliff 200 m high. Immediately before hitting the ground, it was clocked to travel with the speed of 40 m/s. Calculate how much energy was dissipated by the air drag.

Answer 1

First, calculate from energy conservation how much kinetic energy it would have at the bottom without air drag, then subtract from this the actual kinetic energy. That will give the dissipated energy ΔE. Without dissipation, the kinetic energy at the bottom must equal the potential energy at the top.

ΔE = mgh - mv²/2

Plug in

m = 0.1 kg

g = 9.8 m/s²

h = 200 m

v = 40 m/s

and get ΔE in joules.