1. The problem statement, all variables and given/known data A 1.2 kg dynamics cart is rolling to the right along a horizontal lab desk at 3.6 m/s, when it collides head on with a spring bumper that has a spring constant of 2.00 * 10^2 N/m. a) Determine the maximum compression of the spring b) Determine the speed of the cart at the moment that the spring was compressed by 0.10 m. 2. Relevant equations E mechanical = E potential + E kinetic E kinetic = 1/2 m v^2 E elastic = 1/2 k x^2 E gravitational = mgh 3. The attempt at a solution a) I got 0.28 m, and the book agrees. b) The answer should be 1.3 m/s. Here's what I get: Eg is constant, because the height doesn't change. Equal is: Et = Ee + Ek In the previous solution, i set Ee2 + 0 = Ek1 + 0 since before there is no elastic energy and afterwards there is no kinetic energy So Et = 1/2 * 2 * 10 ^2 N/m * 0.28 ^ 2 m ^2 = 7.84 joules Et - Ee = Ek 7.84 J - 1/2 * 2 * 10^2 N/m * 0.10^2 m^2 = Ek = 6.84 J 1/2 * 1.2 kg * v^2 = 6.84 J sqrt(6.84 / 1.2 kg / 0.5) = v^2 = 11.4 m^2 / s^2 Square rooted I get 3.4 m/s The book says I'm doing b wrong, but I don't understand what I did wrong, or if the book is wrong.