# Ballistics Momentum problem

In a ballistics test, a 25.0g bullet traveling horizontally at 1100m/s goes through a 40.0cm -thick 250kg stationary target and emerges with a speed of 900m/s . The target is free to slide on a smooth horizontal surface.

the 1st question of this problem ask: How long is the bullet in the target?

I simply do:

40.0cm=0.4m ; 0.4m/(900m/s)=4.4*10^-4

The answer shows 4.0*10^-4

Did I make a mistake or it is just a rounding problem?

## Answers and Replies

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tiny-tim
Science Advisor
Homework Helper
Welcome to PF!

Hi ZzZerozZ! Welcome to PF!

i] in your distance/speed, you've used the width of the block as the distance, but the block is moving, so the distance is longer

ii] your speed is the final speed, so it's too small

In a ballistics test, a 25.0g bullet traveling horizontally at 1100m/s goes through a 40.0cm -thick 250kg stationary target and emerges with a speed of 900m/s . The target is free to slide on a smooth horizontal surface.

the 1st question of this problem ask: How long is the bullet in the target?

I simply do:

40.0cm=0.4m ; 0.4m/(900m/s)=4.4*10^-4

The answer shows 4.0*10^-4

Did I make a mistake or it is just a rounding problem?
Using s = (u+v)/2 *t the answer is 4 *10^-4. s= distance, u = inital vel, v= final vel.