A driver moving at 20 m s^-1 notices a fallen tree 100 m ahead and applies brakes. What is the minimum magnitude of acceleration required to avoid hitting the tree?
1. Step: u = 20, v = 0, s = 100. 2. Step: 0 = 20^2 – 2 * a * 100 -> 200a = 400 -> a = 2 m s^-2.