Question

A ball of mass x kg and speed y m/s, moves towards a wall and after a perfectly elastic collision starts moving exactly in the opposite direction with same speed. Find the change in momentum​

Answer 1

Answer:

0

Explanation:

Given,

mass of the ball = x kg

velocity of the ball = y m/s

therefore,

initial momentum of the ball = xy

Now,

Since, the ball elastically collided with the wall.

Therefore, final velocity of the ball going towards

the wall will be 0.

Therefore, final momentum of the ball going towards the wall will be 0 ( since, x × 0 = 0 )

Now,

Since its an elastic collision.

Therefore,

Initial momentum + Final momentum = Initial momentum in the opposite direction + Final momentum in the opposite direction

Therefore,

$|xy| + 0 = 0 + |xy| \\ |xy| = |xy|$

Here, the initial momentum of the ball going in opposite direction after collision is 0 because at the time of collision the initial velocity also becomes zero.

And, since the ball starts moving at the same speed in the opposite direction, therefore the momentum also remains same.

Now,

Difference in the momentum in the opposite directions before and after collision is,

$|xy| - |xy| = 0$

Therefore, the answer is 0.

Answer 2

A ball of mass 0.5kg moving with speed of 2.0m/s strikes a rigid wall in a direction perpendicular to the wall and is reflected back after a perfectly elastic collision. If the ball has remained in contact with the wall for 0.5s, calculate the average force exerted on the ball by the wall.





After reflecting back the change in momentum is nothing but 2×initial momentum =2×0.5Kg×2m/s=2Kgm/s

Average force exerted is
Δt
change in momentum
​

Given that Δt=0.5s
so by putting above value we get Force=4N