Archimedes Principle: Calculate Outer & Inner Radii

[grapeape]

Homework Statement

A spherical aluminum ball of mass 1.48 kg contains an empty spherical cavity that is concentric with the ball. The ball just barely floats in water.
A. Calculate the outer radius of the ball.

B. Calculate the radius of the cavity

Homework Equations

Buoyant Force = density of fluid * Volume of object *g

The Attempt at a Solution

 

[Shooting Star]

If the ball barely floats in water, then it's effective density must be vey nearly equal to water. So, equate the mass of the ball to the buoyant force. Also, vol of water = vol of the ball.

 

[Shooting Star]

You'll need the density of Al.