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Homework Help: Archimedes principle

  1. Feb 13, 2012 #1
    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.
  2. jcsd
  3. Feb 13, 2012 #2
    anyone ?
  4. Feb 13, 2012 #3
    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.
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