Homework Help: Physics

Posted by James on Wednesday, March 18, 2009 at 11:29pm.

The hockey captain, a physics major, decides to measure the speed of the hockey puck, He loads a small styrofoam chest with sand, giving it a total mass of 6.4 kg. He places the chest and embeds itslef in the styrofoam. The chest moves off at 1.2 m/s. What was the puck's speed?

I know that the speed is 49m/s.

What was the kinetic energy of the puck before it hit the styrofoam? Not sure how to do this?

What was the kinetic enry of the chest with the puck in it after they moved away. Not sure how to do this?

How much mechanical energy was lost in this ellastic collision? Not sure how to do this either?

Any help on these would be greatly appreciated.

Physics - drwls, Thursday, March 19, 2009 at 12:03am
This looks like a conservation of momentum problem, but this sentence makes no sense:
"He places the chest and embeds itslef in the styrofoam."

I supposes what he is imbeds in the styrafoam and sand chest is the hockey puck, not himself.

It seems to me you need to know the mass of a hockey puck to do this problem. NHL hockey pucks can weigh between 156 and 170 gm. If we use 163 gm,
0.163 Vpuck = (6.4 + 0.2)*1.2 m/s
Vpuck = 49 m/s

That agrees with your "book" answer. The other questions are just number crunching

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