# Homework Help: Momentum and Impulse Cannonball

1. Nov 8, 2009

### hallowon

1. The problem statement, all variables and given/known data
A 2.00X10^2 kg(200kg) shot is discarded horizontally from a cannon of mass 2.0x10^4kg(20000), with a speed of 250 m/s relative to ground.

Find steady force which, acting on the cannon, will stop its recoil in 2.0s
and
How far will cannon recoil

2. Relevant equations
j=fnetxt
conservation of momentum

3. The attempt at a solution
using conservation of momemntum
p= p'
MsVs+McVc = MsVs' + McVc'
0 = MsVs' + McVc'
-msvs'= McVc
and found Vc to be 2.5 m/s backwards,
and using j=fnet t
McVc' = fnet t
fnet =( 20000)(2.5) /2
fnet = 25 000N backwards
so i said steady force was 25 000 N forward needed to stop recoil in 2 seconds
Which im doubtful whether it is right, and do not know how i could find the distance of cannon recoil.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 8, 2009

### jgens

From my calculations, you got the force required to stop the cannon in two seconds correct! Since the problem specifies that the force is steady, you know that the cannon undergoes constant acceleration. Now, do you know any equations that link the acceleration, initial velocity, and distance travelled?

Edit: You also need to know an equation that relates force and acceleration, but that one's easy.

3. Nov 8, 2009

### hallowon

woot found the new reply button -_-

so iguess 2ad = vf^2 -vi^2 i guess huh

thanks for your help :D i was getting worried for nothing :D

4. Nov 8, 2009

### jgens

Looks good to me!