# Momentum Problem on a cannon

## Homework Statement

You load a 100kg cannon with a 10kg cannonball. Initially the cannon is at rest. You fire the cannonball at a velocity of 150m/s.

## Homework Equations

Momentum = mass • velocity

## The Attempt at a Solution

I'm having trouble coming up with the scenario for the problem. The four parts of the equation essentially.
The initial position would be the cannon at rest, so it's not moving.
Velocity = 0. Mass = 110kg.

I would assume the next position would be the cannon firing..
That would mean the velocity is 150m/s going to the right.
At the same time the cannon would move to the left... I'm not quite sure how to split the problem up into 4 scenarios.. I could use a few pointers.

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gneill
Mentor
I'm not sure what you mean here by "scenarios" when it comes to writing an equation. Presumably you're wanting to write an equation for conservation of momentum? But what is it you're trying to determine? You haven't stated what that might be.

Yeah I was trying to write and equation for the conservation of momentum. Im trying to find the velocity of the cannon after it is fired. Forgot to include that, I feel so silly..

gneill
Mentor
Well, before the cannon is fired, both the cannon and the cannon ball are at rest (zero velocity). So what's the initial momentum?

Zero, since momentum = mass*acceleration.

gneill
Mentor
Zero, since momentum = mass*acceleration.
Make that velocity, not acceleration!

Okay, so that's your momentum. It's a conserved quantity, so the total momentum after firing should be zero also. Can you write an equation summing the momenta of the cannon and cannon ball after firing?