1. The problem statement, all variables and given/known data A ball is thrown against a fixed wall where it bounces elastically. The mass of the ball is M and the velocity just before it hits the wall is U. Ignore the force of gravity in this question. a) Does the Principle of Conservation of Momentum apply to this situation? b) Obtain an expression for the change in momentum of the ball in terms of M and U 2. Relevant equations momentum before = momentum after change in momentum = m(v-u) change in momentum= force x time 3. The attempt at a solution I think that the situation does not follow the principle of conservation of momentum, because the situation is just before the ball hits the wall, so there has not been a transfer of momentum yet, but I am still not sure.