Determine the coefficient of friction between a girl's skis and the snow when she skis down a 20° degree hill and her ending speed is exactly two-fifths of what it would have been if the slope had been frictionless.

Answer 1

two-fifths speed, that means KE is 4/25 of all the energy.

find her speed if no friction
mgh=1/2 mv^2
v= sqrt(2gh)
her speed is 2/5 of this , or energy is 4/25 of original energy.
friction energy=mgh(4/25)
mu*cos20*mg*h/sin20=mgh(4/25)
mu=tan20*(4/25) check my work