Doctors see in hypnosis a possible answer to the rejection problem which surgeons meet when transplanting hearts and other organs. For items 11-20, choose the right answer A, B or C to complete the second sentence using the word given, so that it has a similar meaning to the first...Favorite Answer. Momentum IS always conserved. Even collisions between pool balls, momentum isn't 100% conserved either. When they hit, heat and sound is created which is a loss in kinetic energy so velocity speed is lost (even though mass is the same before and after collision).Basically, in a collision like the one you are trying to do, you want an elastic collision, in which both the kinetic energy and momentum are conserved. All momentum (P) is is mass * velocity, and Kinetic Energy (K) is 1/2*mass*velocity^2. In your situtation, I'm assuming everything has the same mass. If so, K = 1/2 * v^2. So, Kf = Ki and Pf = Pi.