1. The problem statement, all variables and given/known data (a) A skier is gliding at 6.75m/s on horizontal, frictionless snow. He starts down an 11deg incline. His speed at the bottom is 21.7m/s. whats the length of the incline? (b) How long does it take him to reach the bottom? I just need help with part (b) 2. Relevant equations a = delta_v / delta_t d=0.5(vf+vi)t 3. The attempt at a solution From part (a), I figured out that a=1.67m/s/s: a=gsin(theta)=1.87m/s/s For part (b), how do I know what kinematics equation to use? 1 - If I use t = vf-vi /a = 7.99s, I get the correct answer. 2 - If I use d=0.5(vf+vi)t, t = 144/0.5(21.7+6.75) = 10.12s, I get the wrong answer. How do I know which equation to use in kinematics problems? All pieces of information are available!