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Homework Help: Need help with physics question

  1. Sep 5, 2004 #1
    I'm really bad at physics and need help with the following question:

    Two spheres are cut from a certain uniform rock. One has radius 4.95 cm. The mass of the other is seven times greater. Find its radius.
  2. jcsd
  3. Sep 5, 2004 #2


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    The average density of an object is:

    [tex]\rho = \frac{m}{V}[/tex]

    Where m is mass and V is volume

    The volume of a sphere is:

    [tex]V = \frac{4\pi}{3} r^3[/tex]

    Where r is the radius.

    These are the only two formulas you need.
  4. Sep 5, 2004 #3


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    Does this look familiar?

    [tex]\frac {R_1}{R_2} = \left(\frac{M_1}{M_2}\right)^{\frac{1}{3}[/tex]
  5. Sep 5, 2004 #4
    Alright, well I got a volume of 508.05 for the sphere with a radius of 4.95, but still not exactly sure of where to go from here.
  6. Sep 5, 2004 #5
    Okay, nevermind, I got the answer at 9.469
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