Question

A trolley of mass 20 kg is at rest on smooth horizontal
surface. A boy throws horizontally one by one 5 kg
sand ball with 20 m/s towards trolley. These sand balls
stick with trolley. How many sand balls should stick
on trolley so that trolley will move with 10 m/s?
[Assume sand ball moved in horizontal direction)​

Answer 1

Answer:

4 sand balls

Explanation:

Let the number of sand balls thrown be n

Then

Momentum imparted by n sand balls = Momentum of the n sand balls and trolley

or, $n\times 5\times 20 = (5n+20)\times 10$

$\implies 100n=50n+200$

$\implies 50n=200$

$\implies n=4$

Therefore, 4 sand balls should stick on the trolley so that trolley moves with 10 m/s

Hope this helps.