okay i have a problem that deals with an elastic collision. so i have the mass of obj A and B and i found the initial velocity of A and B, and i have the final velocity of A and B so now i want to find the change in Kinetic Energy, so i am doing .5(mA + mB)( velocity final ^2) - .5(mA + mB)( velocity initial^2) but what i am confused about is what i am suppose to use for the final velocity and initial velocity. i mean do i just add if initial velocities of obj A and B and use that as Vi, and add up the final velocities of obj A and B and use that as Vf? i dont think that seems right? any help would be great!