puffylover

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Q: suppose the air hockey puck table is not completely frictionless. if the puck loses 6J of energy due to friction, over 05.m of travel, what is the force due to friction on the puck?

A: got it W=Fd

explanation:
"the work-kinetic energy theorem tells us that if 6J of KE were lost, then 6J of work was done on the puck"

so quick question: this whole scenario cannot be compared to the first law of thermo? U=Q-W? Because then I think well the puck slowed down so it must have done work on something.... which is wrong. I'm guessing U=Q-W can only be applied to gases?
 

RogueUnicorn

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the friction work is lost in a mechanical sense, to heat. the surrounding gases, the ice etc capture this energy and their internal energies are increased, but it's not recoverable in this system
 

puffylover

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do u mind explaining that further... i'm still a lil confused... what's doing work on what... the friction (surface) is doing work on the puck right? so what gains internal energy? the puck?
 

loveoforganic

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Both the puck and the ice. The molecules of both move/vibrate slightly more quickly due to the energy conferred from friction.