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Classical Mechanics Level 3

A water heater takes 10 minutes to heat 2 kg of water at 1 5 ∘ 15^{\circ} to 6 0 ∘ 60^{\circ} . Assuming that the input power was 1 watt, what is the efficiency of the water heater?

Submit your answer as x if your answer is x%

Assume the specific heat of water to be 1.

This problem is original and is inspired from the water heater in my bathroom.


The answer is 15.

Mehul Arora by Mehul Arora , 20, India

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1 solution

Aditya Chauhan
Dec 15, 2015

The heat used is = m × s × ∆ T m\times s\times∆T

= 2 × 1 × ( 60 − 15 ) = 90 J 2\times1\times(60-15) = 90J

Power = H e a t / W o r k T i m e \dfrac{Heat/Work}{Time}

= 90 10 × 60 \dfrac{90}{10\times60}

=0.15W

Therefore Efficiency = 0.15 1 × 100 \dfrac{0.15}{1}\times100 = x = 15 \boxed{15}

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