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Question

An object of mass 8 kg falls through a height of 60 m and by means of a mechanical linkage, rotates a paddle wheel that stirs 0.8 kg of water. Determine the change in temperature of water if initial temperature was 15C. Assume no heat is lost to surroundings, specific heat of water, c=4190 J/kgC).

A
0.5C
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B
1.4C
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C
2.1C
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D
3.6C
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Solution

The correct option is B 1.4C
Given that
Mass of object (m)=8 kg
Height of fall (h)=60 m
Mass of water (mw)=0.8 kg
Initial temperature Ti=15C
Loss of mechanical energy E=mgh
Change in temperature of water =ΔT
Thermal energy gained by water E=mwcΔT

From law of conservation of energy,
mwcΔT=mgh
ΔT=mghmwc
ΔT=8 kg×9.8 m/s2×60 m0.8 kg×(4190 J/kgC)
Δ T=1.4C
Hence, the answer (b) is correct.

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