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Homework Help: Help with a mass problem

  1. Nov 8, 2004 #1
    I can't figure out the answer to this problem. Can someone help me please? What would be the weight of a 9 kg mass on the surface of Mars? The mass of Mars is 0.11 that of Earth and its radius is 0.53 that of Earth. answer to this problem. CAn someone help me please?
  2. jcsd
  3. Nov 8, 2004 #2
    weight on earth is determined by mg, and is actually the strength of the gravitational force on the object.

    where g is the accleration due to gravity near the earth's surface.
    the strength of the gravitational force between two objects is Gm(1)m(2)/r^2

    therefor the strength of gravity on a planet, thus the weight of an object, is related to its mass and radius of the planet. hopefully that helps a bit?
  4. Nov 8, 2004 #3


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    The acceleration formula might me more helpful than the force formula

    acceleration = mG * (1/d^2), where m is the mass of the Earth and d is the diameter of the Earth. Since your problem gives you Mars' radius and mass in Earth units, call m and d 1 in the above formula.

    The Gravitational consant G comes in many flavors depending on your units.
    Using Earth = 1 for mass and Earth = 1 for radius, and 9.81 for acceleration at the Earth's surface, plug all these into the above equation and solve for G.

    Then use the same formula with your G, and the given numbers in your problem for Mars' radius (expressed in Earth radii or 0.53) and mass (expressed in Earth Masses or 0.11) to solve for acceleration at Mars' surface.

    Then, with m (9kg) in your problem and your new value for acceleration at the surface of Mars, just use force = mass * acceleration and you'll have your answer in Newtons.
    Last edited: Nov 8, 2004
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