A 1300kg car A stikes a parked 1200kg car B. Car B slides 2m after impact. The coefficient of friction between B's tires and the road is u=0.8. The coefficient of restitution is e=0.4. What is the velocity of A just before impact? I have the equations: mA*vA + mB*vB = mAvA' + mBvB' e = (vB' - vA')/(vA - vB) The initial velocity for B is zero so I still have three variables and only two equations. What other equation do I need to solve this problem? I thought about conservation of energy, but how does friction play into this?