problem: A skier coasts down a hill without initial velocity. The slope is at angle α = 30° with respect to the horizon from p. A to p. B. From p. B to p. C the track is with a reverse angle β = 10° with respect to the horizon. The skier stops at p. C. The motion time for section AB is t1 = 6s, and for section BC - t2 = 15s. Determine the friction coefficient μ between the skies and the snow, as well as the skier's velocity at p. B.

A part of the given solution is: m*y1 = 0 = N1 - m*g*cosα. And I thought that it should be the sin of the angle.

If you could actually explain the solution to the problem, I would really appreciate it.