1 to 2 Interactions, or "explosions" I'm stuck doing this problem on my physics homework.. it's different than the type of problems we have been doing in class, and he hasn't taught us the equation to solve this question. The problem is: Tim, mass 50.00 kg, is riding a skateboard, mass 2.00 kg, traveling at 1.70 m/s. Tim jumps off and the skateboard stops dead in its tracks. With what velocity did he jump? Can anyone tell me what equation to use in order to get the answer?