Homework Help: Bouyant force with water and in equilibrium

1. Nov 9, 2012

bdh2991

1. The problem statement, all variables and given/known data
A cube of wood having an edge dimension of 20.9 cm and a density of 651 kg/m3 floats on water.

what is the distance between the top of the cube to the water level?

2. Relevant equations

F = density*g*Volume

3. The attempt at a solution

I believe i have the right concept down in which i did the sum of the forces so it would be:

-(density of cube*g*Vtotal) + (density of water*g*Vdisplaced) = 0

I would like someone to confirm this for me and i also wanted to ask...couldn't i just use mg for the force of the cube downward and then add the buoyant force of water to it? (if not then why not?)

for example: -mcube*g + (density of water*g*Vdisplaced)

2. Nov 9, 2012

bdh2991

nvm...i complete forgot that d = m/v, therefor the force due to gravity is the same for mg or density*g*volume....sorry about that

3. Nov 9, 2012

SteamKing

Staff Emeritus
Hint: check out Archimedes principle.