1. The problem statement, all variables and given/known data An elastic string of natural length 3.0m can be stretched to a length 4.0m by a weight of mass 10.0kg. Its two extremities are fixed to two points A, B in the same horizontal line at a distance of 4.0m apart, and a mass of 15.0kg is attached to the mid-point. If this mass is released from rest while the string is horizontal, find the velocity of the mass when it has descended a distance of 1.5m 2. Relevant equations 3. The attempt at a solution F = kx 10g = k(1) k = 10g 15g = 10gx x = 1.5m (Maximum stretched length of the string) When the mass has fallen a distance of 1.5m, the string is stretched to the length 2(1.52+22)1/2= 5 Thus, stretched length of the string = 1m 0.5(10g)(1.5)2=0.5(10g)(1)2+0.5(15)(v2) v = 2.86m/s However, the answer is 3.13m/s. Where did I go wrong?