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

A rifle bullet loses 1//20th of its velocity in passing through a plan

1.	A rifle bullet loses 1//20th of its velocity in passing through a plank. What willbe the least number of such planks required to just stop the bullet?
Answer» Solution :For one plank `u=u,V=u-(u)/(20)=(19)/(20)u` `((19v)/(20))^(2)-v^(2)=2ax.......(1)` For n planks `u=u, v=0` `0^(2)-v^(2)=2anx…..(2)` Dividing (2), (1) `n=(-v^(2))/(((19)/(20)v)^(2)-v^(2))=(1)/(1-((19)/(20))^(2))` `=(20xx20)/((20+19)(20-19))=(400)/(39)=10.3` implies so, 11 planks are REQUIRED. The BULLET shall stop in 11 th plank