Question

A bullet moving at 20 m/sec. it strike a wooden plank and pentrates 4 cm before coming to stop. the time taken to stop is

• A. 0.08 sec
• B. 0.16 sec
• C. 0.004 sec
• D. 0.02 sec

Answer 1

The correct option is C 0.004 sec

Given,

$u=20m/s$

$s=4cm=0.04m$

$v=0m/s$

From 3rd equation of motion,

$2as=v^2-u^2$

$2\times a\times 0.04=0^2-20\times 20$

$a=-\frac{20\times 20}{2\times 0.04}$

$a=-5000m/s^2$

From 1st equation of motion,

$v=u+at$

$0=20-5000t$

$t=\frac{20}{5000}=0.004sec$