A quantity of hot water at 100oC is added to 400g of water at 10oC...

WAEC 2015

A quantity of hot water at 100^oC is added to 400g of water at 10^oC until the temperature of the mixture is 60^oC.

Calculate the mass of the hot water added. [Specific heat capacity of water =4200JKg^-1 K^-1]

A. 200g
B. 320g
C. 400g
D. 500g

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Correct Answer: Option D

Explanation

Heat lost by hot water = Heat gained by cold water

M x 4200 x (100 - 60 = 0.4 x 4200 x (60 - 10)

4200m x 40 = 0.4 x 4200 x 50

40m = 0.4 x 50

m = \(\frac{0.4 \times 50}{40}\) = 0.5kg

= 500g

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