A nonconducting container filled with 25 kg of water at 20°C is fitted with a stirrer, which is made to turn by gravity acting on a weight of mass 35 kg. The weight falls slowly through a distance of 5 m in driving the stirrer. Assuming that all work done on the weight is transferred to the water and that the local acceleration of gravity is 9.8 m·s−2, determine: (a) The amount of work done on the water. (b) The internal energy change of the water. (c) The final temperature of the water, for which CP = 4.18 kJ·kg−1·°C−1.
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A nonconducting container filled with 25 kg of water at 20°C is fitted with a stirrer,
which is made to turn by gravity acting on a weight of mass 35 kg. The weight falls
slowly through a distance of 5 m in driving the stirrer. Assuming that all work done
on the weight is transferred to the water and that the local acceleration of gravity is
9.8 m·s−2, determine:
(a) The amount of work done on the water.
(b) The internal energy change of the water.
(c) The final temperature of the water, for which CP = 4.18 kJ·kg−1·°C−1.
(d) The amount of heat that must be removed from the water to return it to its initial
temperature.
(e) The total energy change of the universe because of (1) the process of lowering
the weight, (2) the process of cooling the water back to its initial temperature, and
(3) both processes together.
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