Hi,

Question

A squash ball of mass 0.035 kg hits the wall at speed of 78 m/s and
rebounds straight back at 61 m/s. The ball is in contact with the wall for
0.44 s.
a) What is the original momentum of the squash ball? 2.73 kg-m/s

b) Calculate the impulse imparted to the ball by the wall.
deltap=mdeltav
deltap=0.035kg*17m/s= 0.595kg-m/s

c) What force acted on the squash ball from its impact?
deltap/t=f
0.595kg-m/s/0.44s=1.35N

I'm fairly certain b & c are wrong but I don't know what to change...
Thanks for your help

Answer 1

b. impulse=changemomentum= m(vf-vi) now remember, then the change of velocity is in opposite directions, so impulse=m(61+78)
c. force= impulseAbove/timeonWall

Answer 2

b) impulse is the change in momentum ... final minus initial
... look at your deltav value ... velocity is a vector ... magnitude AND direction

this should also "fix" c)

Answer 3

So to make sure I understand...
Because it's bouncing back off the wall & change in velocity is now negative I should have used impulse=m(-change in velocity)
impulse=0.035kg*-(-61-78)
impulse=0.035kg*139m/s
impulse=4.9 kg-m/s
Is that right?
Thanks!

Answer 4

yes.