# Bullet hitting stationary Target.

A bullet of 0.005 kg travelling at 20m/s penetrates deeply into a fixed target and is brought to rest in 0.01 sec. The distace through which it penetrates is:

I used,

acceleration= V/t
= 20/.01
a = 2000 m/sec sq

Distace covered = Ut+0.5 at^2
= 20*0.01+0.5*2000*(o.o1)^2
S= 30cm.

Is it correct or any other solution is possible..?

The initial speed and the acceleration have opposite directions.

@willem2:

How is tat? can you plz elaborate.

gneill
Mentor
Does the bullet slow down or speed up as it moves through the block? So is acceleration positive or negative?

Acceleration reduces as the bullet enters the target.

so acceleration is negative......

gneill
Mentor
so acceleration is negative......

The velocity reduces as it passes through the target. So yes, acceleration is negative (in the direction opposite to the velocity).

I understand ur point. So is the approach right? And how about answer?

gneill
Mentor
The approach is fine. How about the answer? Have you calculated one with the new knowledge about the acceleration direction?