What is the initial speed of a bullet fired into a ballistic pendulum?

[balling12]

Homework Statement

A 7.0-g bullet is fired into a 1.5-kg ballistic pendulum. The bullet emerges from the block with a speed of 200 m/s, and the block rises to a maximum height of 12.6 cm. Find the initial speed of the bullet.

Homework Equations

The Attempt at a Solution

I used the equation:
(Mbullet)(Initial Velocity)+(Mpend)(Initial Velocity)=(Mb)(Fvelocity)+(Mp)(Fvelocity)
Once i plugged in all of the information i have i came to the answer of 306.5 but it is incorrect.

 

[Doc Al]

Conservation of momentum applies to the collision of bullet and block, but how did you make use of the maximum height? (You'll need a second equation.)

 

[balling12]

Conservation of momentum applies to the collision of bullet and block, but how did you make use of the maximum height? (You'll need a second equation.)

For my second equation i used (.5mvf^2)-(.5mvi^2)= -(mgyf-mgyi)
when i solved: vf=.49

 

[Doc Al]

For my second equation i used (.5mvf^2)-(.5mvi^2)= -(mgyf-mgyi)
when i solved: vf=.49

Show exactly how you got that result.

 

[balling12]

Show exactly how you got that result.

Initial V Of Pend= 0 Initial Height of Pend= 0
so (.5)mvf^2= -mgyf
masses cancel
vf= square root[ (2)(g)(0.0126)]
=.49

 

[Doc Al]

Initial V Of Pend= 0 Initial Height of Pend= 0
so (.5)mvf^2= -mgyf
masses cancel
vf= square root[ (2)(g)(0.0126)]
=.49

12.6 cm = 0.126 m (not 0.0126).

 

[balling12]

12.6 cm = 0.126 m (not 0.0126).

dang that was my problem lol. thanks