question_answer 19)

A trolley of mass 300 kg carrying a sandbag 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 trolley's floor at the rate . What is the speed of the trolley after the entire sand bag is empty ?  

Answer:

As the trolley carrying the sandbag is moving with uniform speed of 27 km/h, so no external force is acting on the trolley + sandbag system. When the sand leaks out, it does not cause any external force to act on the system. Hence the speed of the trolley remains unchanged even after the sandbag becomes empty.