As shown in fig. two identical balls strike a rigid wall with equal speeds but a different angles of incidence. They are reflected back without any lose in speed.


(a) Determine the direction of force exerted by each ball on the wall.
(b) Determine the ratio of impulse imparted by the two balls on the wall in both cases.

Explanation

(a) Force on a body acts in a direction of change in its momentum. In both cases change in momentum of ball is along XO. Hence, in both the cases force will be along x-direction on the wall.
(b) Case(a)
Momentum of the ball before reflection=`mv(along OX)`
Momentum after reflection `=-mv(along XO)`
Now, I=change in momentum of ball
`=-mv-mv=-2mv(along OX)=2mv("along x")`
Hence, implse on wall will be 2mv(along OX)
Case(b) Similarly `I'=-mv cos theta-mv cos theta=-2mv cos theta`

Ratio `=(I)/(I')=(2mv)/(2mv cos theta), (I)/(I')=(1)/(cos theta)`.