Solved: Calculating Force Needed for Archimedes' Principle

[suzukits]

Homework Statement

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?

Homework Equations

P = F/A
Fb = ρgV
ρ = m/V

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.

 

[suzukits]

anyone ?
please

 

[LawrenceC]

For starters look at the equation below that I copied.

800 = m / 0.000025

You have an error with your units.

Are you familiar with Archimedes Principle? If so, please state it.