1) A skier with a mass of 70 kg is traveling down a slope of 15 degrees at an acceleration rate of 0.2 m/s^2.

What is the coefficient of friction between the skis and the snow?

2) A football player pushed a 60 kg blocking sled with a constant horizontal force of 400 N. The coefficient of kinetic friction between the sled and ground is 0.5. How much horizontal force opposes the forward motion of the sled? What is the sled's horizontal acceleration? (assume that the playing surface is level).

3) How much impact force is exerted on the knee if the mass of your body (56 kg) is accelerating towards the ground at a rate of 22 m/s^2?