I need explanation! please! QUESTION 38*** This and the following question conce

Question

I need explanation! please!

QUESTION 38***

This and the following question concern the same physical situation.

A ball of mass M is released from rest a height H above the floor and collides elastically with the floor. What is the magnitude of the impulse exerted by the floor on the ball during the collision?

(a)   M sqrt(2gH)
(b)   2 M sqrt(2gH) <--answer
(c)   0

QUESTION 39**

Suppose instead that the ball is released from rest from the same height but sticks to the floor. Compared with the previous problem, the impulse exerted by the floor on the ball will now be

(a)   the same.
(b)   greater.
(c)   less.<--answer

QUESTION 40*

An object initially at rest explodes into two equal pieces. Below are two possible pictures of the pieces after the explosion, where the arrows indicate the direction of the velocity of each piece. Which of these is possible?

I need explanation! please! QUESTION 38*** This and the following question concern the same physical situation. A ball of mass M is released from rest a height H above the floor and collides elastically with the floor. What is the magnitude of the impulse exerted by the floor on the ball during the collision? (a) M sqrt(2gH) (b) 2 M sqrt(2gH)

Explanation / Answer

1.

Impulse is change in momentum.

velocity before elastic collison is sqrt(2gh) in downward direction and after collison it is sqrt(2gh) in upward direction, so the difference would be 2*sqrt(2gh) . this will be multiplied by mass M which results to M*2*sqrt(2gh) .

2.

If the balls sticks to ground , final velocity is zero. So change in momentum will be  M*sqrt(2gh) . which is half the previous case. so lees than part 1.

3.

Only B is the right choice.

Because the object was at rest so its initial momentum was 0., which should be conserved. Velocity in same direction couldn't add up the momnetum to be zero but velocity in opposite direction can do that.

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