State reason for the following : (a) A person is hit harder, when he falls on a hard floor than when he falls on sand or cotton.(b) A gunman gets jerk in backward direction while firing a gun (c) A bullet fired on a glass window makes a fine hole while a stone smashes when hits it. 

For all the above it is due to conservation of momentum
lets look
a) as the ground is hard solid when a person fall on it what happens he gets injured because his momentum suddenly decreases and but in case of sand and cotton he gain some relaxatation time for his momentum to became slow steady okkay

b) same here when bullets get fired suddenly increase of momentum of bullet lets the gun to gets recoil velocity (backward momentum produce) so gunmen feel jerk.

c) But here is about pressure as u know pressure=(force/area) i.e., pressure is inversily proportional to area
  Here is the story as bullet has sharp end or you can say less area of contact with glass that means high pressure so it easily penetrate in the glass or say wood as compare to stone which has area when his the glass
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