Question

A bullet moving with a velocity of 100 m/s can just penetrate two planks of equal thickness. The number of such planks penetrated by the same bullet, when the velocity is doubled, will be

• A. 4
• B. 6
• C. 8
• D. 10

Answer 1

The correct option is C

8

Let initial velocity of bullet be and it can just penetrate number of planks. Final velocity should be zero. Let thickness of each plank be x.

$v^2=u^2-2aswheres=nxThus,2anx=u^{2}orn\alpha u^{2}therefore,\frac{n_1}{n_2}={\left(\frac{u_1}{u_2}\right)}^2=\frac{1}{4}or{n}_2=4n_1=4\times 2=8$