WAEC Physics 2015 Objective — Question 19
Question 19 of 50 from the West African Examinations Council (WAEC) Physics 2015 Objective paper, with the correct answer and a full explanation.
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A quantity of hot water at 100°C is added to 400 g of water at 10°C until the temperature of the mixture is 60°C. Calculate the mass of the hot water added. [Specific heat capacity of water = 4200 J kg⁻¹K⁻¹]
- A. 200 g
- B. 320 g
- C. 400 g
- D. 500 gCorrect
Explanation
Heat lost by hot water = heat gained by cold water: M(4200)(100−60) = 0.4(4200)(60−10), giving M = (0.4×50)/40 = 0.5 kg = 500 g.
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