# Cannonball velocity problem

1. Nov 10, 2008

### sweedeljoseph

1. The problem statement, all variables and given/known data
A 30 kg cannonball strikes a 150 kg stationary wooden block and embeds itself in the block. The block and cannonball move together at 4 m/s. What was the original velocity of the cannonball?

2. Relevant equations
m1v1=m2v2

3. The attempt at a solution
using the equation i gave i got:

30v=150(4)
v=20

the answer my teacher my teacher gave me was 24 m/s. and i was thinking if you add the '4 m/s' to the velocity i just found it would be '24 m/s'. but i dont know if that was right. i was thinking it might be right because they both moved together after the ball hit the wood for 4 m/s. so is that right? or am i supposed to do something else?

thank you!
sweedeljoseph

2. Nov 10, 2008

### Physics197

The mass after the collision would be the masses of both objects added together since they are now considered to be one object moving at the same velocity.

m1V1 + m2V2 (equals 0) = v'(m1 + m2)

Solve for V1 before

3. Nov 10, 2008

### sweedeljoseph

so i was right? you add the '4 m/s' to the velocity that i found?