A plate of mass `M` is held at rest by firing bullets from below. Each bullet has a mass `m`, velocity `u` (up) just before hitting and stops after hitting the plate for a moment and falls. Determine the number of bullets striking the plate Fig. per unit time

Explanation

The change in moment of a bullet due to hitting the late is `vec/_\p=0-vec"mu"`. If `N` bullets be hitting the plate per unit time, the rate of change of momentum of the bullets is `-Nvecm u`. This is also the fore exerted by the plate during collision. Using Newton's third law of motion, an opposite force `Nvecmu` will act on the plate due to the collidign bullets.
`Nvec"mu"+vecMg=0`
`implies N"mu"=Mg`
`N=(Mg)/("mu")`

This is the number of bullets striking the plate per unit time.