10kg of hot water in a bucket at 70∘C is cooled for taking a bath adding to it 20kg water at 20∘C. What is the temperature of the mixture?(Neglect the thermal capacity of the bucket)
A
30.67∘C
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B
36.67∘C
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C
60.67∘C
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D
46.67∘C
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Solution
The correct option is B36.67∘C By the energy conservation, thermal energy lost by hot water = thermal energy gained by cold water
If Tf be the final temperature of mixture, mhS(Th−Tf)=mcS(Tf−Tc) where S= specific of water
or mhTh−mhTf=mcTf−mcTc
or mhTh+mcTc=Tf(mh+mc)
or Tf=mhTh+mcTcmh+mc=[(10)(70)+(20)(20)]10+20=36.67oC