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Hydrostatic force

  1. Sep 24, 2015 #1
    1. The problem statement, all variables and given/known data
    An object made entirely from one material has a volume of 30m3. It floats in a liquid of density of 3g/cm3 with only half its mass below the liquid's surface. The object is then placed in another liquid of same volume but with a density of 1g/cm3 If the final upthrust that will act on the object is expressed in the form of [tex] a × 10^{b} N [/tex] give the value of a and b. [Assume g = 10m/s2]

    The answer stated is 3 × 103

    I got a different solution, please kindly advice.

    Thanks :)

    3. The attempt at a solution

    Hyrdostatic force is : ρVg = 3 g/cm3 × 1000 cm3/m3 kg/g × 15m3 × 10 N/kg = 450'000 N

    Since hydrostatic force = gravitational force,

    The mass of the object will be : m = 45000N × 0.1 kg/N = 4500kg
    The density of the object will be: ρobject = 4500kg/30m3 = 1500 kg/m3

    Since it is denser than the second liquid, the hydrostatic force experienced in the second liquid will be as follow:

    F= ρVg = 1 g/cm3 × 1000 cm3/m3 kg/g × 30m3 × 10 N/kg = 300'000N = 3 × 105 N
    Last edited: Sep 24, 2015
  2. jcsd
  3. Sep 24, 2015 #2


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    Your answer of 3 ×105 N looks correct to me.
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