Calculate Force (Free Fall)?

Question

A 35 g ball released from rest falls vertically. It hits the ground and remains in contact with it for .5 ms. Rebounding elastically, it returns to its original height. The whole trip takes 8 s. Calculate the average force on the ball during contact with the ground.

Answer 1

Impulse = change in momentum

First we need to know how fast the ball is going when it hits the floor. For this we use kinematics:

h = 1/2 g t^2

h = 1/2 ( 9.8 m/s^2 ) ( 4 sec ) ^2

Solve for h, the height from which the ball was released.

Now we can get the speed:

2 a h = v^2

2 ( 9.8 m/s^2 ) ( h ) = v^2

Solve for v^2

At last we have the change in momentum. Just before the impact, it was mv down; just after, it's mv up. So the the change in momentum is 2mv. Impulse is force over time so

F t = 2 m v

You know the contact time is .5 ms; solve for the average force F.

Answer 2

Don't forget to take the 0.5 ms off the 8 seconds for the whole journey.

Detail is important!

Answer 3

rigidity = Mass x acceleration for loose falling products their acceleration is by means of gravity. Gravity = 9.8 m/s^2 so in case you realize the products mass then you definately can calculate the rigidity.