1. The problem statement, all variables and given/known data A solid cube of foam plastic has a volume of 25m^3 and a density of 800kg/m^3. How large a force is required to hold it under water? 2. Relevant equations P = F/A Fb = ρgV ρ = m/V 3. The attempt at a solution ρ = m/V 800 = m / 0.000025 m = 0.02kg so F = mg = 0.02 x 9.8 = 0.196 I understand that the force required to keep it under water will be greater than this but I'm having a hard time finding the right equation.