Question: On a frictionless, horizontal air table, puck A (with mass [tex]m_1[/tex]) is moving toward puck B (with mass [tex]m_2[/tex]), that is initially at rest. After the collision, puck A has a velocity of [tex]v_1[/tex] to the left, and puck B has velocity [tex]v_2[/tex] to the right. 1. What was the speed of puck A before the collision? My answer to this part of the question was correct. It is [tex](m_2*v_2)/(m_1) - (v_1)[/tex]. 2. Calculate the change in the total kinetic energy of the system that occurs during the collision. I think this depends on the first part of the question. So, I'm thinking: [tex]\Delta K= K_f - K_i[/tex] [tex](1/2)(m)(v_f^2 - v_i^2)[/tex] I should sum up the velocities, right? [tex](1/2)(m_1+m_2)((v_2 - v_1)^2 - ((m_2*v_2)/(m_1) - (v_1))^2)[/tex] But, that is not correct.