Question

A bullet moving with a velocity of 200 cm/s penetrates a wooden block and comes to rest after traversing 4 cm inside it. What velocity is needed for travelling distance of 9 cm in same block?

• A. 100 cm/s
• B. 136.2 cm/s
• C. 300 cm/s
• D. 250 cm/s

Answer 1

The correct option is C

300 cm/s

As $v^2=u^2-2as\Rightarrow u^2=2as(\because v=0)\Rightarrow u^2\propto s\Rightarrow \frac{u^2}{u^1}={\left(\frac{s_2}{s_1}\right)}^{1/2}\Rightarrow u_2={\left(\frac{9}{4}\right)}^{1/2}{u}_2=\frac{3}{2}{u}_1=300cm/s.$