# Question about momentum involving shooting a hockey puck

1. Dec 18, 2008

### meeklobraca

This is not homework, just a curious question.

What would need to be figured out, to determine how fast a hockey player would have to shoot the puck at a goalie, for the goalie to be forced backwards about 5 feet. The idea was being floated about if a player could shoot a puck so fast that the puck and the goalie would go into the net effectivly being a goal.

2. Dec 18, 2008

### buffordboy23

Interesting question. I imagine that you are familiar with basic physics formulas?

Here are some ideas for starters:
1. There is a small coefficient of friction between the ice and the goalie's skates. You could assume that the total energy needed is W = Fd = (uN)d = (umg)d.
2. You could relate this to the kinetic energy equation, K = 1/2mv^2, to determine the needed velocity v. You may be disappointed with the result using just the ideas from 1 and 2, since you don't see these results to be true.
3. When the puck impacts with the goalie, this will produce a torque about the goalie's center of mass.

Another idea is to compute the required torque necessary to overcome the friction of the ice/skates and knock the goalie flat on his back and go from there.

Last edited: Dec 18, 2008