What was the original speed of the bullet?

[Joyci116]

Homework Statement

A 10.0g bullet is fired into a stationary block of wood (m=5.00 kg). The bullet imbeds into the block. The speed of the bullet-plus-wood combination immediately after the collision is 0.600 m/s. What was the original speed of the bullet?

ball m=10.0g=0.01kg
wood m= 5.00kg
Vf=0.600m/s
Vi=?

Homework Equations

p=mv

The Attempt at a Solution

i=change in momentum
=mVi-mVf
So, solve for Vi?
Then I would have to know what i is, right?

Thank you.

 

[gneill]

Write equations for the momentum before and after the collision takes place. Be sure to specify which masses are involved.

 

[Joyci116]

p=mv
The momentum found using final velocity:
p=(0.01kg)(0.600m/s)=0.006 kg*m/s (ball)
p=(5.00kg)(0.600m/s)=0.006 kg*m/s (wood)
And I assumed the initial velocity was zero, so I ended up with a zero momentum.
Is that correct so far?

 

[lightgrav]

no, the bullet started with (fast) unknown velocity
It was theonly thing that HAD momentum, at first.

 

[Joyci116]

Thanks, I finally figured it out. :D