# Volume Submerged

jerick232002
1.) What is the density of a piece of wood that floats in water with 70% of its volume submerged?

2.) calculate the density of a person who floats in water with 5% of her volume above the surface?

JaredJames
I assume this is a school work question and so you're going to have to show some working before we can help.

jerick232002
i don't know how. i think first to do is to look for the value of mass? and then?please help me..

JaredJames
Well the questions aren't about finding an exact solution, you need to rearrange the equations, inserting any known values and then you will come out with a ratio.

jerick232002
the exact solution is d=m/v?right? but the only given is the percent, volume?what im going to do?first step?

JaredJames
Density = Mass / Volume

For an object to float, it has to displace an amount of water equal to it's weight. In this case, when 70% of the wood is submerged, that amount of water equals the weight of the wood.

So how can you put all of this together with equations and come up with a way of expressing the volume?

jerick232002
Mass = 1000 g /Volume??

JaredJames
When weight of object = weight of water displaced the object floats.

Weight of object = mg = weight of water displaced = mg

Density = Mass / Volume

Mass = Density x Volume

Weight of object = DwoodVwoodg

Weight of water displaced = Dwater0.7Vwoodg

So you get:

DwoodVwoodg = Dwater0.7Vwoodg

You can take out gravity:

DwoodVwood = Dwater0.7Vwood

You can also cancel out Vwood:

Dwood = 0.7Dwater

D = Density, V = Volume, g = gravity