(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 Fav is given by
Total power consumed by 4 devices
= 4 x 500 = 2000 W = 2 kW
Time for which devices run = 10 hours
Energy consumed per day = 2 x 10 = 20 kW h
Energy consumed in the month of November i.e., 30 days
= 20 x 30 = 600 kW h
(b) When a body falls freely under gravity, it has an acceleration g. Its velocity and hence its kinetic energy also goes on increasing at the lowest point, the body strikes the ground. A part of its energy is converted into sound energy and other into heat energy.