Question

A bullet, on penetrating two successive wooden planks
of unequal thickness, loses its velocity by 200 m.s-1 in
each case. If the initial velocity of the bullet is
1000 m. s-1, calculate the ratio of thickness of the
planks.
[9:7]
​

Answer 1

Given that,

Loses of velocity = 200 m/s

Initial velocity of bullet = 1000 m/s

After penetrating first block,

Final velocity  is

$v_{f}=1000-200$

$v_{f}=800\ m/s$

For second block,

Initial velocity is 800 m/s

Final velocity  is

$v_{f}=800-200$

$v_{f}=600\ m/s$

We need to calculate the thickness of first block

Using equation of motion

$v^2-u^2=2as$

Put the value into the formula

$1000^2-800^2=2as$

$as=\dfrac{1000^2-800^2}{2}$

$as=18000\ m/s$....(I)

We need to calculate the thickness of second block

Using equation of motion

$v'^2-u'^2=2as'$

Put the value into the formula

$800^2-600^2=2as'$

$as'=\dfrac{800^2-600^2}{2}$

$as'=14000\ m/s$.....(II)

We need to calculate the ratio of thickness of the  planks

Using equation (I) and (II)

$\dfrac{as}{as'}=\dfrac{18000}{14000}$

$\dfrac{s}{s'}=\dfrac{9}{7}$

Hence, The ratio of thickness of the  planks is 9:7

Answer 2

Explanation:

See my answer.

IF I AM CORRECT, PLEASE MARK ME AS A BRAINILIST!