Question

A bullet can penetrate a wooden block with its kinetic energy. How many wooden blocks it can penetrate if its velocity becomes 4 times then its initial velocity

Answer 1

16 blocks

v² = u² + 2 a S

, take the thickness of a block to be x, and as the bullet passes through the block with a velocity v its ke reduces and velocity becomes zero...

mathematically,

0 = v² - 2 a x

when we take v as initial velocity and x as the thickness of block. Keep in mind a is negative as bullet is retarded.

so v²= 2ax

x= v²/2a  = constant k

take second case when velocity is four times the initial.

16v² = 2 ax

x= 16 k (we take k to be the thickness of one block)

so math tells us 16 times one block,

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