Question

A ski jumper glides down a 30.0 degrees slope for 80.0 ft before taking off from a negligibly short horizontal ramp. If the jumpers takeoff speed is 45.0 ft/s, what is the coefficient of kinetic friction between skis and slope?

Answer 1

friction force up slope = mu m g cos 30

work done by friction = -80 mu m g cos 30

drop in height = 80 sin 30 = 40 ft

potential energy drop = m g (40 ft)

ke = (1/2) m v^2

so
(1/2)m(45)^2 = 40 m g - 80 mu m g cos 30

1012 = 40(32) - mu * 32 * 69.3

1012 = 1280 - 2218 mu

mu = (1288 - 1012)/2218 = .124

Answer 2

Ah