Answer to Question #17436 in Mechanics | Relativity for hugyu

Question

A bullet moving with a speed 'v' can just penetrate two planks of equal thickness. Find the number of such planks that the bullet will penetrate if its speed is doubled.

Answer 1

The energy of the bullet will increase
N =& (m(2V)²/2) / (mV²/2) = (2V)² / V² = 4

times if its speed is doubled. So, the bullet will penetrate 4 times more planks, that is

M = 2*4 = 8

such planks.