1. The problem statement, all variables and given/known data Question: First image My working: Second image I used Va+Vb for the speed of separation. I got the answer for (a), but couldn't get the answer for (b). I know the proper expression is "Vb-Va" with Vb being negative. But if I use Vb-Va, (a) would be wrong. How come? 2. Relevant equations Principle of conservation of momentum, Newton's Experimental Law. 3. The attempt at a solution As shown in the second image.