cannonball velocity problem

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

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

sweedeljoseph

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