# Homework Help: Buoancy force question

1. Mar 5, 2010

### lbella026

1. The problem statement, all variables and given/known data
A cube made from iron has sides equal to 20cm/side. The density of iron is 7860kg/m^3. The cube is completely submerged in water; the density of water is 1000kg/m^3. What is the buoancy force acting on the cube.

2. Relevant equations
W(DL)= (D(L))(V)(g)

3. The attempt at a solution
W(DL)=(1000kg/m^3)(8000cm^3)(10m/s^2) =8x10^7 Neutons
Im not sure if this answer is correct ????

2. Mar 5, 2010

### Galileo

Take care of your dimensions. You're using the density in kg per meter^3, but volume in cm^3.
1 Newton is 1 $kg m s^{-2}$ You can get the right units from there.
When in doubt, always use SI-units.

3. Mar 5, 2010

### ehild

Force of buoyancy = weight of the water displaced by the cube. How can that small cube of water weight 8x10^7 newtons?

Think, what is your weight? less or more than 8x10^7 N? Your average density is also very close to 1000 kg/m^3. Are you bigger or smaller than that 20x20x20 cm^3 cube?

ehild