Chapter 7, Problem 14Q

(a)

To determine

To identify: Whether the momentum of the ball conserved during any part of the given process.

Answer to Problem 14Q

Momentum will not be conserved in any part of the given process.

Explanation of Solution

Introduction:

According to the conservation of momentum principle, the total momentum before and after the collision must remain constant.

When any object falls upon the surface of Earth, it is not only falling with its constant velocity but it is falling with a variably increasing velocity. This variable is the gravitational force acting on the object along with its previous velocity.

Here, when a superball falls from a height $h$ then, it will gain its momentum with the gravitational force acting along with it downwards, which attracts it towards the hard steel plate (fixed to Earth). Also, when going upwards, with the recoiling velocity, gravitational force will act along. This time gravity will attract it downwards, causing deceleration of the ball going upwards.

Conclusion:

Hence, neither when falling upon the hard steel plate nor when going upwards after collision, momentum will be conserved.

(b)

To determine

The parts of the process where momentum is conserved for Earth-ball system.

Answer to Problem 14Q

Momentum will be conserved in the entire process.

Explanation of Solution

Introduction:

According to the conservation of momentum principle, the total momentum before and after the collision must remain constant.

When both superball and hard steel plate are considered to be in the internal system of Earth, then the ball coming downwards and then going upwards after the collision will act in the force of gravity. Thus, the momentum of this system will be conserved in the entire process.

Conclusion:

Therefore, the entire system will conserve the momentum.

(c)

To determine

The parts of the process where momentum is conserved for Earth-ball system if the ball is replaced with a piece of putty that falls and sticks to the steel plate.

Answer to Problem 14Q

Momentum will be conserved in the entire process.

Explanation of Solution

Introduction:

According to the conservation of momentum principle, the total momentum before and after the collision must remain constant.

When the ball is replaced with a piece of putty, the entire system is considered to be the internal system of Earth. Hence, putty and hard steel plate both will act with the force of gravity only. After the collision, putty will stick with the plate due to adhesive properties causing momentum of the entire system conserved before and after the collision.

Conclusion:

Thus, the total momentum will remain conserved.