Answer to Question #260849 in Mechanics | Relativity for Jake

Question

A rifle bullet can penetrate one plank. If the velocity of the bullet be tripled, how many planks it will penetrate ?

Answer 1

Explanations & Calculations

• It is the same process as the question you posted under number 260441.
• The resistivity from a plank as well as the mass of the bullet is considered constant.
• Assuming the planks remain intact during penetration and length of a plank to be $\small L,$

$\qquad\qquad \begin{aligned} \small \frac{1}{2}mv^2&=\small fL\cdots(1)\\ \\ \small \frac{1}{2}m(3v)^2&=\small fx\cdots(2)\\ \\ \small (2) \div(1),\\ \\ \small \frac{(3v)^2}{v^2}&=\small \frac{x}{L}\\\\ \small x&=\small 9L \end{aligned}$

• Penetration of 9 plnaks is possible.