Question

Imagine you're trying to change the course of an incoming ball, heavy ball. The ball is rolling toward you, and you've got a big whiteboard that you can use to either hit the ball so it moves in the opposite direction, hold still so that it bounces off, or "catch" the ball by moving the whiteboard in the opposite direction of the ball's motion as it comes into contact with the ball. If your goal was to minimize the impact the ball had on you (and the whiteboard), which one would you choose and why?

Answer 1

We know, impact is equal to Force multiplied by time , which is equal to change in momentum, now if we see clearly to reduce the impact created by the ball we simply have to reduce the momentum of the ball , and to reduce the momentum we had reduce the speed of the ball by which it is coming.

Now if we will hit the ball, its speed will not decrease and thus the impact will not believe less.

Also if we hold the cardboard still then the ball will strike the cardboard and will again bounce , here after the ball strike the cardboard the speed of the ball will became less but still it will not be minimum. Thus in this condition also the impact will not be minimum.

Now if we catches the ball, then here the ball comes to rest and the speed of the ball become zero, thus the momentum became zero. Due to this change in momentum the impact will be minimum. Thus in order to reduce the momentum to minimum we will catch the ball.