Kinetic energy , K=1/2mv^2
So,
K?v^2
If initial velocity is u,
the final velocity will be v=u/?2
(as the kinetic energy is half on its initial value)
Given ,
penetration distance, d=6cm
Using,
V^2-u^2=2aS, or u^2/2-u^2=2a(6) or a=-u^2/24
Now,
the bullet penetrate further distance d with initial velocity v=u/?2
before coming to rest.
Thus,
final velocity is zero.
So,. 0^2-(u/?2)^2=2ad
or
-u^2=2(?u^2/24)d
d=6cm
