Sand drops vertically at the rate of 2 kgs–1 on to a conveyor belt moving horizontally with a velocity of 0.1 ms–1. The extra power needed to keep the belt moving is

Force required to keep the belt moving = rate of increase of horizontal momentum of sand = mass per seconddmdt× velocity change =2×0.1=0.2 NPower = Force ´ velocity=0.2×0.1=0.02 W