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]​

(1) 5
(2) 4
(3) 2
(4) 10

Answer 1

Answer:

2 is the answer for your question

Answer 2

Answer:

Option (2) 4

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.