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Question

A 10kW drilling machine is used to drill a bore in a small aluminium block of mass 8kg. Find the rise in temperature of the block in 2.5 minutes,assuming 50% power is used up in heating the machine itself or lost to the surroundings.
(Specific heat of aluminium=0.91Jg1oC1)

A
100oC
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B
103oC
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C
150oC
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D
155oC
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Solution

The correct option is A 103oC
Here,P=10kW=104W,m=8kg
time,t=2.5minute=2.5×60=150s

Specific heat,s=0.91Jg1C1

Total energy =P×t=104×150=15×105J
As 50% of energy is lost,

Energy available,Q=12×15×105=7.5×105J

AsQ=msT
T=Qms=7.5×1058×103×0.91103oC

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