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A bullet loses ` 1//20` of its velocity in passing through a plank. What is the least number of plank required to stop the bullet .A. (a) ` 8`B. (b) ` `7`C. (c ) ` 11`D. (d) ` 14` |
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Answer» Correct Answer - C Let (u) be the initial velocity of bullet and (a) be the retardation of bullet while passign through a plank. Velocity of bullet after passing theough plank ` v= u - u/(20) = (19 u)/(20)` Taking motion of bullet through one plank and using the relation, ` v^2 =u^2 +2 as`, we hve (19)/(20) u)^@ = u^2 -2 aS` or ` 2 aS =u^2 - ((10)/(20)u)^2` [ :. motion is retarted ]` ` 2 a S=u^2 - ( 361)/(400)u^2 = (39u^2)/(400)` ltbRgt Taking motion bullet through (n) plaks ` ` v=0, S=n S` ` 0 u^2 -2 a nS` or ` n=u^2/(2 aS0 = u^2 /( 39u^2 //400) = (400)/(39) = 10.25 ~~ 11`. |
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