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Homework Help: Finding Mass of a Sphere

  1. Mar 21, 2010 #1
    1. The problem statement, all variables and given/known data
    A sphere of metal has a radius of 5.3 cm and a density of 8.15 g/cm3. What is the mass of the sphere? Answer in units of g.

    2. Relevant equations

    Volume of a sphere=4/3лr^3

    3. The attempt at a solution
    I found the volume by multiplying 4/3 by л and 5.3 squared. I got 66.1850323. I plugged this into the formula for density, manipulated it to get mass by itself and got 539.4118513. This answer seems really unreasonable. I think I need to do some conversions but I'm not sure what to convert. I think I need to convert the radius to meters but the density is in grams/cm cubed and I need to answer in units of grams.
    Last edited: Mar 21, 2010
  2. jcsd
  3. Mar 21, 2010 #2
    Mass = density times volume

    First, volume of a sphere is 4/3[itex]\pi[/itex]r^3.

    Next, don't convert anything you've been given the right units for what you've been asked for. Produce a volume for the sphere in terms of cm^3, then

    [itex]cm^3[/itex] * [itex]\frac{g.}{cm^3}[/itex] = [itex]g.[/itex]
    Last edited by a moderator: Feb 26, 2015
  4. Mar 21, 2010 #3
    So you're saying find the volume. I got 623.6145193 cm^3. Then I multiply that by the density (8.15) to get the mass. I get 5082.458333. That doesn't seem right. XD
  5. Mar 21, 2010 #4
    But it is. Wow. You're amazing! Thanks! XD
  6. Mar 21, 2010 #5
    Glad to help.

    Remember that the equation of finding the mass of a sphere is

    Mass = density times volume
    Last edited by a moderator: Feb 26, 2015
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