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Physics - Buoyant Force

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A piece of metal weighs 50.0 N in air, 36.0 N in water, an 41.0 N in an unknown liquid. Find the density of the unknown liquid.

  • Physics - Buoyant Force - ,

    find volume of metal first
    Buoyant force in water = 14 N = weight of water displaced in 1 g gravitational field
    mass of water displaced = 14 N/9.8 m/s^2 = 1.43 kg of water displaced
    the density of water = 1,000 kg/m^3
    so
    volume of metal = 1.43*10^-3 m^3

    Buoyant force in unknown = 50 - 41 = 9 N
    so mass of unknown displace = 9/9.8 = .918 kg

    so the density of unknown = .918kg/1.43*10^-3 = 642 kg/m^3
    or 64.2% of the water density

  • Physics - Buoyant Force - ,

    I'm confused about the "1 g gravitational field". What's the 1 g referring to and why is it 1 g?

  • Physics - Buoyant Force - ,

    g is the acceleration of gravity which is about 9.8 m/s^2 on the surface of earth.
    Since the weights were given in Newtons, a unit of force, not mass, I used weight in Newtons = mass in kilograms * acceleration in meters / second squared to find the mass in kilograms.

  • Physics - Buoyant Force - ,

    where did you got the buoyant force in water?

  • Physics - Buoyant Force - ,

    It's well known it doesn't need to be given (like the gravitational force)

  • Physics - Buoyant Force - ,

    Take the actual weight (in air) of the object and subtract the weight(apparent) the objects seems to have in the unknown fluid ie take 50N and subtract 36N to get 14N which is the buoyant force/upthrust.

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