text: physics help? on a frictionless horizontal air table, puck a (with mass 0.371 kg) is moving toward puck b (with mass 0.251 kg), which is initially at rest. after the collision, puck a has velocity 0.121 m/s to the left, and puck b has velocity 0.652 m/s to the right.  what was the speed v_ai of puck a before the collision?  calculate deltak, the change in the total kinetic energy of the system that occurs during the collision. use the conservation of momentum.  calculate the momentum of puck a and momentum of puck b after the collision.  do a vector addition of this momentum to get the total momentum of puck a before the collision.  this will give you the velocity of puck a before the collision allowing you to calculate the kinetic energy before the collision.  you also have the velocity and masses to calculate the kinetic energy after the collision.  equations: momentum  is mass * velocity energy is mass * velocity ^ 2 / 2