Question

A bullet incident normally on a wooden plank loses one tenth of its speed in passing through the plant the least number of such planks required to stop the bullet

Answer 1

velocity looses = 1/10th

1/n =1/10

n=10

no.of planks =n²/2n-1

=(10)²/2(10)-1

=100/20-1

=100/19

=5.26

approximate value = 6

Answer 2

Answer:

Concept:

Relative speed refers to the speed of a travelling body in relation to another. The difference between two substances travelling in the same direction is used to compute their relative speed. However, when two bodies are travelling in opposite directions, the relative speed is calculated by adding their speeds together. The difference between relative speed and relative velocity is that relative speed is a scalar quantity, whereas relative velocity is a vector quantity.

Given:

When a bullet hits a wooden plank, it loses a tenth of its speed as it passes through the plant with the fewest such bullets.

Find:

find the planks required to stop the bullet

Answer:

Let the thickness of one plank be s, and the planks be positioned in such a way that the bullet is stopped.

$hence, V=0$

here $V^{2} =V_{0}^{2} +2as*n$  

$0 = V_{0} ^{2} + 2ans$

$n={(-V_{0}^{2} )/(2as)$

bullet loses $(1/10)th$ of velocity  

∴ $V = (9 / 10)V_{0}$

going through a plank at a high velocity

∴ ${(9 / 10)V0}^2 = V0^2 + 2as$

${(-19) / (100)}V0^2 = 2as$

pulling in equation

$n = [{-V0^2} / {- V0^2(19 / 100)}]$

  $= {(100) / (19)}$

  $= 5$

∴  planks required to stop the bullet is 5

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