$(a)$ Define average power. Calculate the total energy consumed in the month of November in a household in which four devices of power $500\, W$ each are used daily for $10\, hours.$
$(b)$ $A$ freely falling object eventually stops on reaching the ground. What happens to its energy?

(N/A) Average power is defined as the average rate of doing work. If a total work $W$ is done in a time $t,$ then average power $P_{av}$ is given by:
$P_{av} = \frac{W}{t}$
Total power consumed by $4$ devices $= 4 \times 500 = 2000\, W = 2\, kW$
Time for which devices run $= 10\, hours$
Energy consumed per day $= 2\, kW \times 10\, h = 20\, kWh$
Energy consumed in the month of November ($30$ days) $= 20\, kWh \times 30 = 600\, kWh$
$(b)$ When a body falls freely under gravity,it possesses kinetic energy due to its motion. When it strikes the ground,its kinetic energy is dissipated into other forms of energy,primarily sound energy and heat energy,due to the impact with the surface.