A ball of mass m is dropped on to a floor from a certain height The collision is perfectly elastic and the ball rebounds to the same height and again falls. Find the average force exerted by the ball on the floor during a long time interval.
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2 Answers
For the total time, the change in momentum is zero.....
Because initial momentum was zero.. and the final momentum is also zero...
Avg force is total change in momentum by total time...
so the answer is zero....
But during this whole time there was change in momentum due to gravity and due to the floor..
The average force = avg force by gravity+ avg force by the floor..
avg force by gravity is mg (downwards)
hence the avg force by floor is mg (upwards)
Disclaimer: in the abvoe question some of you may not be convinced that the initial, final momentum is zero.. what you can otherwise think is that the initial and ifnal momenum are finite.. while the time is very large hence the avg force is zero...