Calculating Submarine Recoil Speed from Torpedo Launch

[mikefitz]

A submarine of mass 2.3 times 106 kg and initially at rest fires a torpedo of mass 260 kg. The torpedo has an initial speed of 100.9 m/s. What is the initial recoil speed of the submarine? Neglect the drag force of the water.

My work:

Pi=Pf
Pi=0
Pf= Mtorpedo * Vtorpedo - Msub * Vsub

Vsub = (260kg * (100.9 m/s) ) / 2.3 x 10^6

I get Vsub = .0114 m/s

Why is this wrong?? Thanks

 

[Doc Al]

Looks OK to me. Why do you think it's wrong?

 

[mikefitz]

Stupid online homework system, I had to take the answer out a few more decimal places.

Thanks for your help Doc Al, appreciate it.