Problem with buyoancy and fluid stuff

[Daniel]

I can't figure this out... I know that answer is wrong, help please? Someone? Ahh!

http://www.gatcity.com/images2/physics.jpg

 

[enigma]

I guess it's because I haven't TA'd anything yet...

Can you put down how you went about solving the problem here so we can find where you're having trouble?

Thanks

 

[Daniel]

TAed?

I figured I needed to find the mass of the wood raft, and then if I had that I could solve what the Fb was.. Originally I thought the buyoant force was 1158 since the net force equals zero and there is a force of 1158 pushing down (that should be 1158 * 9.81)

... and then after that I just got really confused and talked to a friend from my class who was equally confused...

If I can find the mass, then I know that (1158 + m)/(3.40) = density, but I just can't figure out that mass. I've tried all of the buyoant formulas I know, and they aren't helping much...

 

[Doc Al]

Ask yourself what are all the forces acting on the "pig plus raft" system. You know it's in equilibrium, so the net force is zero.

I see three forces acting:
Weight of the pig (acts down)
Weight of the raft (acts down) - how do you figure its weight?
Bouyant force of water on raft (acts up) - how do you figure bouyant force?

First figure out all these forces as much as you can. Then write the equation for equilibrium. Then solve for what you don't know.