You throw a tennis ball against a brick wall. The ball rebounds with a speed equ

Question

You throw a tennis ball against a brick wall. The ball rebounds with a speed equal to the original speed, but it is now moving in the opposite direction. Note that the brick wall is rigid enough that it does not deform at any time. Answer the following questions:

Which is true about the momentum of the tennis ball?
There is not enough information to tell.
It IS conserved.
It is NOT conserved.

Which is true about the momentum of the brick wall?
There is not enough information to tell.
It IS conserved.
It is NOT conserved.

Assuming that the wall only interacts with the ground and the ball, which is true about the magnitude of the impulse from the ground on the wall?
There is not enough information to tell.
It is negligible compared to the magnitude of the impulse from the wall on the ball.
It is greater than the magnitude of the impulse from the wall on the ball.
It equals the magnitude of the impulse from the wall on the tennis ball.
It is less than the magnitude of the impulse from the wall on the ball.

Explanation / Answer

Momentum is conserved

Let
m = mass of ball
M = mass of wall
vin = initial velocity of the ball
vfin = final velocity of the ball

Vin = initial velocity of wall = 0
Vfin = final velocity of wall

Then mvin +0 = mvfin + MVfin

and vfin = -vin ---> MVfin = 2mvin --> the ball bounces back with the same speed, but opposite velocity

The change in momentum of the ball is m( vin - vfin) = 2mvin
The change in momentum of the wall is M(Vin - Vfin) = - 2mvin

The magnitude of the momentum change is the same, the direction is obviously opposite, that is why you get the - sign.

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.