A water heater of power 2000W is used to heat water. The specific...

Heat provided to water will be responsible for increase in temperature. Therefore, we can write

$η \times P \times t = M \times s \times \DeltaT$

Now, $η = \dfrac{70}{100} = 0 . 7$ and $\text{energy} = \text{power} \times \text{time}$.

Therefore,

$t = \dfrac{2 \times 4200 \times \left(60 ° - 10 °\right)}{0 . 7 \times 2000}s = 300s$