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A bullet loses ` 1//2th1 of its velocity is passing through a plank. What is the least number of planks required to stop the bullet ? |
Answer» Let (u) the initial velocity of butter and (a) be the retardation of the bullet while passing through a plank. Velcoty of bullet after passing through a plank is ` u =u - u//20 = 19 u //20` Taking motion of bullet through one pland and using the relation, `v^2 =u^2 = 2 a S, we have ` (19 u //20 )^2 -2 aS1 or ` `2 aS= u^2 - (36 1//400) u^2 = 39 u^2 //400` Let (n) number of plands be required to stop the bullet. Taking motion of bullert through (n) planks, we have ` ` u =u, v= 0, S= nS. a=-a, then` ` O^2 =u^2 -2 a Sn` or ` n= u^2 / (2 a S) = u^2 /((39u^2//400) = (4000/(39) ~~ 11`. |
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