Problem 8: In a crude attempt to repeat Joule’s famous experiment you begin with

Question

Problem 8: In a crude attempt to repeat Joule’s famous experiment you begin with 1 kg of water at room temperature in a not very well insulated container. You stir the water until a thermometer shows that its temperature has increased by 1 K. In the process you did 5000 J of work on the water by stirring it. What was the magnitude of the thermal energy transfer |Q| from the water to the surroundings while you stirred? Note: the specific heat capacity of water is 4.2 J/g/K.

A) 0 J                    B) 800 J

B) 4200 J                    D) 5000 J

E) insufficient information given to determine |Q|

Explanation / Answer

thermal energy = W -Q

Q = mcdT

dT =1

c = 4.2 J/g/k

m = 10^3 g

Q = 4200 J

thermal energy = 5000 - 4200 = 800 J

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