A ball of mass m approaches a wall of mass M ( m) with speed 4 m s- 1 along the normal to the wall. The speed of the wall is 1 m s- 1 towards the ball. The speed of the ball after an elastic collision with the wall is -

Question

A ball of mass m approaches a wall of mass M (> > m) with speed 4 m s- 1 along the normal to the wall. The speed of the wall is 1 m s- 1 towards the ball. The speed of the ball after an elastic collision with the wall is - (A) 5 ms- 1 away from the wall (B) 9 ms- 1 away from the wall (C) 3 ms- 1 away from the wall (D) 6 m s- 1 away from the wall

Tardigrade Admin · Accepted Answer

<img class="img-fluid question-image" alt="Solution" src="https://cdn.tardigrade.in/q/nta/p-nd8lai8roj9zoplh.jpg" /> Let v be the velocity of ball after collision, collision is elastic ∴ e =1 or relative velocity of separation=relative velocity of approach ∴ v- 1=4+1 or v=6 m / s (away from the wall)

Q. A ball of mass m approaches a wall of mass $M (>> m)$ with speed $4 m s^{- 1}$ along the normal to the wall. The speed of the wall is $1 m s^{- 1}$ towards the ball. The speed of the ball after an elastic collision with the wall is -

$5 m s^{- 1}$ away from the wall

$9 m s^{- 1}$ away from the wall

$3 m s^{- 1}$ away from the wall

$6 m s^{- 1}$ away from the wall

Let $v$ be the velocity of ball after collision, collision is elastic
$∴ e = 1$
or
$re l a t i v e v e l oc i t y o f se p a r a t i o n = re l a t i v e v e l oc i t y o f a pp ro a c h$
$∴ v - 1 = 4 + 1$
or $v = 6 m / s$ (away from the wall)

Q. A ball of mass m approaches a wall of mass M(>>m) with speed 4ms−1 along the normal to the wall. The speed of the wall is 1ms−1 towards the ball. The speed of the ball after an elastic collision with the wall is -

5ms−1 away from the wall

9ms−1 away from the wall

3ms−1 away from the wall

6ms−1 away from the wall