A62.0-kg skier is moving at 6.30 m/s on a frictionless, horizontal, snow-covered plateau when she encounters a rough patch 4.90 m long. the coefficient of kinetic friction between this patch and her skis is 0.300. after crossing the rough patch and returning to friction-free snow, she skis down an icy, frictionless hill 2.50 m high.

Here are the missing questions:
(a) How fast is the skier moving when she gets to the bottom of the hill?
(b) How much internal energy was generated in crossing the rough patch?
Part A
The initial kinetic energy of the skier is:

Part of this energy is then used to do work against the force of friction. Force of friction on the horizontal surface can be calculated using following formula:

The work is simply the force times the length:

So when the skier passes over the rough patch its energy is:

When the skier is going down the skill gravitational potential energy is transformed into the kinetic energy:

So the final energy of the skier is:

This energy is the kinetic energy of the skier:

Part B
We know that skier lost some of its kinetic energy when crossing over the rough patch. This energy is equal to the work done by the skier against the force of friction.

It is increased due to the doppler effect. (apex)