Chapter 9.2, Problem 35SSC

(a)

To determine

To Identify:The system used in catching a heavy ball while oneis standing on a skateboard and standing on a ground.

Explanation of Solution

Introduction:

As per Newton's third law of motion, action and reaction forces are in pair.When you catch the ball on skateboard, the balls reaction force applies on you due to which skateboard moves..

In first case the ball is catched on skateboard. So skateboard \and catcher are isolated system.

In second case as the heavy ball is catched on the ground that is on earth.

Conclusion:

Skateboard and catcher form an isolated system.

(b)

To determine

To determine using law of conservation of momentum the backward rolling of a you after catching the ball and while standing on a skateboard and no movement while catching the ball.

Explanation of Solution

Introduction:

According to Law of conservation of momentum total momentum before catching the ball should be equal to total momentum after catching the ball.

During first case the ball is catched on skateboard and the catcher rolls backward. Here, the ball transfers the momentum to skater and skateboard. Hence, the momentum is conserved.

In second case, as the heavy ball is catched on the ground that is on earth. As earth's mass is larger than ball, so change in velocity is almost zero. Therefore, in second case momentum is not conserved.

Conclusion:

Momentum is conserved in first case and in second case momentum is not conserved.