Q. A bullet moving with a speed of can just penetrate into two planks of equal thickness. Then if speed is doubled, what will be the number of such planks?

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A

B

C

D

Solution:

Let retarding force is uniform and it is
So,by work energy theorem
We get, .......(i)
Now, let required plank are , So again by work energy theorem

By putting value from (i)
We get

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