We just started learning Conservation of Momentum, and I feel completely lost. This is the following question I was asked: 1. The problem statement, all variables and given/known data A 2.00-kg object moving at 6.00 m/s collides with a 4.00-kg object that is initially at rest. After the collision, the 2.00-kg object moves backward at 1.00 m/s. This is a one-dimensional collision, and no external forces are acting. a) Calculate the velocity of the 4.00-kg object after the collision. My attempt was to simply use the Momentum equation: 2. Relevant equations & The attempt at a solution mA1vA1 + mB1vB1 = mA2vA2 + mB2vB2 So: vB2 = (mA1vA1 + mB1vB1 - mA2vA2)/mB2 Resulting in the velocity to be 3.5m/s. I was just looking for someone to confirm that answer, because I am unsure if I did it right. In question b) it asks: Calculate the velocity of the centre of mass of the two objects (i) before the collision and (ii) after the collision. What does that mean? Thank you for helping.