Question

A bullet moving at 20 m/sec. It strikes a wooden plank and
penetrates 4 cm before coming to stop. The time taken to stop is... (in
sec)​

Answer 1

Explanation:

Given,

u=20m/s

s=4cm=0.04m

v=0m/s

t=?

From 3rd equation of motion,

2as=v

2

−u

2

a=

2s

v

2

−u

2

a=

2×0.04

0

2

−20×20

a=−5000m/s

2

From 1st equation of motion,

v=u+at

0=20−5000t

5000t=20

t=

5000

20

t=0.004sec