posted by Mara .
A 0.105-kg hockey puck moving at 20 m/s is caught and held by a 77-kg goalie at rest. With what speed does the goalie slide on the ice?
One would not expect a goalie in front of the net to NOT have his skates parallel in a "free to slide" position. A goalie needs to be able to push his body forward and from side to side on short notice. They must want you to apply conservation of momentum and assume no friction, but that is a poor assumption in this situation. Here is what they expect you to use, even though is it is not accurate:
(Initial puck speed)(Puck mass)
= (combined mass)*(final goalie velocity)