Problem $2$: Energy Conservation in a Non Conservative System $($Ch$.7)$ A skier of mass m $=70$kg starts from rest at the top of a hill of height h $=50$m$.$ The skier slides down the hill and reaches the bottom at a speed of v $=25$m$/$s$.($a$)$ Determine the total work done by friction during the skier$$s descent. $($b$)$ If the coefficient of kinetic friction is $$k $=0\mathrm{.}15,$ calculate the length of the slope.