1. The problem statement, all variables and given/known data Magnetic puck A, with a mass of 0.100 kg, is pushed towards stationary 0.050 kg magnetic puck B, to cause a head-on collision. You may neglect friction. The initial velocity of puck A is 12 m/s [E]. Puck B moves with a velocity of 14 m/s [E], after the collision. a) Find the velocity of puck A after the collision. 2. Relevant equations p=mv pinitial=pfinal Einitial = Efinal Ek = 1/2mv^2 3. The attempt at a solution Basically I understand how to solve the question using the momentum by why is that I get a different velocity when using the energy? Since friction is neglected, where could this system be losing kinetic energy? I did Ei=Ef which is Eki=Ekf 1/2(0.100)(12)^2+0=1/2(0.100)v_A^2 + 1/2(0.050)(14)^2 I end up getting 6.8m/s for the final velocity of puck A But the correct answer is 5.0m/s I tried to plug that into the equation but I get 7.2J=6.15J which is incorrect. What am I doing wrong here?