Floating Wood: Finding the Ratio Above Water

[gaily4]

A block of wood with a density that is 750 kg/m3 is floating in a tank of water. How much of the wood is above the surface of the water



D=M/V



I've been trying for hours to try to figure this one out. The only info I'm given the the density of a block of wood in the water at 750kg/m^3. I'm thinking that it has something to so with the approx. density of water at 1000kg/m^3, so the ratio is 4:3 so that approx 25% would be above the water, but not at all sure I'm on the right track.

 

[gneill]

You're on the right track. Now all you need to do is derive it :-)

Why not try a strictly symbolic approach. Let the density of the wood be r1 and that of the water r2. Now suppose the volume of the block is v. What's the weight of the block? How much water needs to be displaced for it to float? ...

 

[tiny-tim]

welcome to pf!

hi gaily4! welcome to pf!

hint: find all the forces on the wood (and remember that force = https://www.physicsforums.com/library.php?do=view_item&itemid=80" times area)

 

[gaily4]

thank you ...I think I get it!