# Pressure of balls bouncing on area

a 5g balls fall dropped from 3m bounces up 1m. if 100 such balls fall on an area of 2m^2 every second what is the average pressure exerted by the balls?

ive tried to solve this problem 100 different ways and i cant get the answer (3Pa).

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dav2008
Gold Member
LoN, you wouldn't happen to have a Physics 213 midterm tonight at 7pm, would you? ;)

Pressure is force/area and force is (change in momentum)/time. You're provided with the area and time, so all you have to find is the change in momentum of the ball as it hits the surface.

haha yes i do. small world eh i must not be setting this up right, heres what im doing.

1/2 m v^2 = mgh solve for v for each height, 1 m and 3m.

then find the change in momentum by multiplying the vs i have solved for by the mass of the ball and subtract. i get .0162 for the change in momentum. so then i multiply that by 100(?) and divide by 2m^2 and i end up with .81Pa :yuck:

where am i screwing up dav2008
Gold Member
Remember that the momentum as the ball is going down is negative, and the momentum as the ball is going up is positive.

Good luck tonight!

thanks for the help, what a lame mistake i was making :grumpy: