Calculating Buoyancy Force for Iron Cube Submerged in Water | Homework Solution

[lbella026]

Homework Statement

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.

Homework Equations

W(DL)= (D(L))(V)(g)

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 ?

 

[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.

 

[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