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Q & A: height to heat

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Most recent answer: 10/22/2007
Q:
I just gave my school exam and in the question paper there was this question : water falls from a height of 50 meters. what is the rise in temperature of water.(C =4.2J/gram degree Celsius g = 10m/s2) I wasn’t able to answer this question and hope you can answer it for me.
- jayveer parekh (age 15)
india
A:
I'm guessing that the idea was that the water splats onto the ground, and that you're supposed to assume that all the kinetic energy of it falling gets converted to internal thermal energy. (In a real situation, some of the energy would leave into the ground or as sound waves, so this calculation will overestimate the actual heating somewhat.)

One kilogram starts with 50 meters*1kg*10m/s^2 = 500 Joules of potential energy. That converts to kinetic energy, then to thermal energy. With a specific heat of 4.2 J/ C-gm, the heat capacity is 4200 J/ C. So it sounds like around 0.24 C is the answer.

Mike W.

(published on 10/22/2007)

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