A skateboarder is competing in the half-pipe event at the Olympics. He reaches the top of the half pipe at a vertical velocity of 10 m/s. His total mass is 70 kg. a) Calculate the kinetic energy of the competitor when he leaves the half pipe. Ignore the effects of friction. Ek = 0.5mv^2 Ek = 0.5*70*100 Ek = 3500J = 3.5KJ Here's where i'm not so sure... b) If frictional forces of 100 N were acting on the skateboarder, what height would he reach. Okay so once he leaves the pipe the only two forces which are pulling him down are gravity and this frictional force Fg = 70*9.8 = 686N 686N + 100N = 786N So now i'll find the acceleration -Ff = ma -786 = 70*a a = -11.23m/s^2 V2 - V1 = a*t 0 - 10 = -11.23*t t = 0.89s d = v1t + 0.5at^2 d = 10*0.89 + 0.5*-11.23*0.89^2 d = 4.45 meters I have a feeling i'm doing something illegal here, or just not right. Is this ok?