# Bullet kinematics to find velocity

1. Jan 6, 2006

### nrc_8706

A(n) 6g bullet is fired into a 253g block that is initially at rest at the edge of a frictionless table of height 2m. the bullet remains in the block, and after impact the block lands 2.1m from the bottom of the table. g=9.8m/s^2. find the initial speed of the bullet

all in know is that....... Pi=Pf
m1Vi1=(m1+m2)Vf

do you use kinematics to find velocity final?

2. Jan 6, 2006

### andrewchang

You use kinematics to find the initial velocity of the block in the horizontal direction, and then use that value in momentum to find the velocity of the bullet.

3. Jan 6, 2006

### nrc_8706

from what i understood of what you replied.......

t=(2h/g)^.5=.638

Vx=x/t=3.291m/s

4. Jan 6, 2006

### andrewchang

yes, that is correct. now, once you know the final velocity after the inelastic collision between the bullet and the block, you can find the original velocity of the bullet.

5. Jan 6, 2006

### nrc_8706

so i plug in 3.291m/s into the first equation?

6. Jan 6, 2006

### andrewchang

yup, that's right.

7. Jan 6, 2006