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Volume help

  1. Aug 8, 2005 #1
    im having a really hard time trying to figure this out.
    An ore sample weighs 19.8 N in air. When the sample is suspended by a light cord and totally immersed in water, the tension in the cord is 11.5 N.

    Find the total volume of the sample.
    Take the density of water to be rho_water = 1000 kg/m^3 and the free fall acceleration to be g = 9.80 m/s^2.

    heres the equation i figured out for this type of problem.

    force of buoyancy=density*volume* gravity.

    alright is the force of buoyancy for air and water 19.8 and 11.5 respectively?
    if so wont i just have to multiply grvity times thhier densities divided by the force to find the volumes then add them up?
  2. jcsd
  3. Aug 8, 2005 #2


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    You can neglect the buoyancy for air - it's neglible.
    The difference in tension in the cord is 19.8 - 11.5 = 8.3 N.
    The displacement of the water by the mass has provided this buoyancy force (8.3N)

    now use the eqn you worked out.
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