Answer:
V * ρB = WB volume of ball * density of ball = weight of ball
V * ρW = Ww volume of ball * density of water = buoyant force
ρB / ρW = WB / Ww = 80 / 20 = 4 water provides 20 N of buoyant force
ρB = 4 ρW = 4 gm/cm^3
ρW = 1000 kg / m^3 = 1 gm / cm^3
(1 gm/cm^3) = .001 kg / .000001 m^3 = 1000 kg/^3
ρW = 1 gm / cm^3
multiply by 9.8 or 980 to get weight densities
In this case
4 * 1000 kg/m^3 * 9.8 m/s^2 = 39200 N /m^3 weight density of ball
