If P = mv, then P^2/(2m) is: I know the answer is Kinetic Energy, I just don't know the proof. Help? A 70kg man and his 40kg daughter stand together on skates in the middle of a frozen lake. They push apart. Immediately after the push the father has an initial velocity of .8 m/s in on direction and his daughter has an initial velocity of v in the opposite direction. Find the magnitude of v, the daughter's speed: The question continues to ask for other variables and the like, which I could all calculate if I knew the daughter's speed, which I can not figure out. Please do help.