A rifle bullet loses 1/20th of its velocity i | vedclass

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Question

(c)Let the thickness of one plank is $s$ if bullet enters with velocity $u$ then it leaves with velocity 

$v = \left( {u - \frac{u}{{20}}} \ri

Vedclass · Accepted Answer

$11$

Vedclass · Answer

(c)Let the thickness of one plank is $s$ if bullet enters with velocity $u$ then it leaves with velocity 

$v = \left( {u - \frac{u}{{20}}} \right) = \frac{{19}}{{20}}u$ from ${v^2} = {u^2} - 2as$ 

$&rArr;$ ${\left( {\frac{{19}}{{20}}u} \right)^2} = {u^2} - 2as$

$&rArr;$ $\frac{{400}}{{39}} = \frac{{{u^2}}}{{2as}}$ 

Now if the n planks are arranged just to stop the bullet then again from ${v^2} = {u^2} - 2as$ $0 = {u^2} - 2ans$ 

$&rArr;$ $n = \frac{{{u^2}}}{{2as}} = \frac{{400}}{{39}}$

$&rArr;$ $n = 10.25$ As the planks are more than $10$ so we can consider $n = 11$

A rifle bullet loses $1/20th$ of its velocity in passing through a plank. The least number of such planks required just to stop the bullet is

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