What is the mass density of a submerged cylinder?

[cyclemun]

Homework Statement

A 6.40 cm-tall cylinder floats in water with its axis perpendicular to the surface. The length of the cylinder above water is 1.00cm.

Homework Equations

What is the cylinder's mass density?

The Attempt at a Solution

Well, I am confused because I can use the equation for buoyancy to find the mass of the cylinder, but I don't know how to find its volume.

 

[Defennder]

You don't need the radius of the cylinder to find the volume. The question only asks for its density. Just write out the equation using 'r' to denote the unknown radius and something will cancel out.

 

[cyclemun]

so would i use the forumula F = rho* V * g?

 

[bowma166]

The way I would go about doing this problem--I don't know if it's the best way--is to say the cylinder has a mass m, then figure out the volume of water needed to equal this mass. You can then equate this to a formula for mass of the cylinder.

 

[Defennder]

so would i use the forumula F = rho* V * g?

You still need to break V up in terms of r and h.

 

[rl.bhat]

Weight of the cylinder= Area*6.4 cm*density*g
Weight of the displaced water= Area*5.4*1000*g
Now find the density.

 

[talaroue]

I have the same problem just different numbers... I am confused on what to do. F=rho*v*g
then after you cancel out you get
F=mhg right? is that the force on the bottom?

 

[RTW69]

For a floating object the fraction of the volume of a floating object that is below the fluid surface is equal to the ratio of the density of the object to the density of the fluid:

V-f/V-o=rho-o/rho-f as has been noted, the radius cancels, you know rho-f, you can solve directly for rho of the object.