What is the speed of the skier on reaching the bottom of the slope?

Question

A 60-kg skier starts from rest from the top of a 50-m high slope. If the work done by friction is -6.0 * 10^3 J, what is the speed of the skier on reaching the bottom of the slope?

Answer 1

Energy at start = PE = mgh = 29,400 Joules

6000 Joules is "lost" to friction.

29,400-6000 = 23,400 J can be used to give the skier kinetic energy (KE) = 1/2 m*v^2,

This 1/2 m v^2 = 23,400 and v=28 m/s (2 sig. figs)

-Fred

There are other ways to do this problem, but this is probably the "easiest".

Note: You can use an energy conservation approach or a "Big 4" kinetics or Newtonian approach.  It's the same physics and you'll get the same answer.  It's a matter of taste and your "comfort" using each approach.