Bullet kinematics to find velocity

[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?

 

[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.

 

[nrc_8706]

from what i understood of what you replied...


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

Vx=x/t=3.291m/s

 

[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.

 

[nrc_8706]

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

 

[andrewchang]

yup, that's right.

 

[nrc_8706]

gracias for all your help