Compute Density & Buoyancy: Metal & Plastic

[JJBrian]

Homework Statement

apparent mass of the metal weight in air = 100g
apparent mass of the metal weight in water = 75g

a)Compute the buoyancy force. From this, compute the volume of the metal. Compute the density of the metal. The density of aluminum is 2.7 g/cm3, of iron is 7.9 g/cm3, and of gold is 19.3g/cm3. Is your metal mostly aluminum, iron, or gold?
b)The mass of a plastic sphere is 110g. Calculate the buoyancy force and use it as above to compute the
density.

The Attempt at a Solution

F bouyancy = density water * vmetal*g
Fbouyancy = Mdw*g

Fbouyancy = (Mmetal in air - Mmetal in water)
Fbouyancy =( 100-75)(9.8) = 245g*m/s^2
F bouyancy = density water * vmetal*g
245g*m/s^2 = 1g/cm^3 *Vmteal*9.8m/s^2
Vmetal = 25cm^3
p = m/v
p = (100g/25cm^3)
p=4g/cm^3
I not too sure if this is correct...
I don't know how to do part b)

 

[ehild]

Your result is correct.

ehild