Question

A bullet starts with a speed u, enters into a wall and after penetrating a distance x acquires a speed v. It goes a further distance y before it comes to rest. Show that , v/u=(y/y+x)1/2

Answer 1

Answer:

Initial KE= K. (let)

Let after penetration distance S1 against frictional force of penetration acting per unit length f, the loss of energy=f S1

Loss of KE =K/3^2

(Since 1/3 of the velocity is lost)

Thus fS1=K/9……..(1)

Remaining KE=K2=8K/9

It is used for further penetration S2

Therefore fS2=8K/9……..(2)

from equation 1 and 2 we get

S2=8 S1

=8×4cm

=32 cm