A trolley of mass 300 kg carrying a sand bag of 25 kg is moving uniformly with, a speed of 27 km/h on a frictionless track. After a while, sand starts leaking out of a hole on the , floor of the trolley at the rate of 0.05 kg. What is the speed of the trolley after the entire sand bag is empty?
In present problem, there are no net external forces. The sand is slowly leaking downwards from the hole. Consequendy, normal reaction acting vertically upwards also slowly decreases. But it does not do any work because it is at right angle to trolleys motion. Thus, there is no change in speed of the trolley and it will continue among moving with a uniform speed of 27 kmh.