A bullet loses 1/20 of its velocity in passing through a plank What is the least number of planks required - Physics - Motion In A Straight Line

Question

A bullet loses 1/20 of its velocity in passing through a plank
What is the least number of planks required to stop the bullet?

Panchali Dutta · Accepted Answer

Let the thickness of the plank be s m

Initial velocity = v m/s

Final velocity after one plank = 19v/20 m/s

$(\frac{19 v}{20})^{2} - v^{2} = 2 a s$

Let the number of planks required to stop the bullet be n

$\Rightarrow 0 - v^{2} = 2 n a s$

$\Rightarrow n = - \frac{v^{2}}{(\frac{19 v}{20})^{2} - v^{2}} = 10.25$

The bullet will definitely stop by the eleventh plank.

A bullet loses 1/20 of its velocity in passing through a plank.What is the least number of planks required to stop the bullet?