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Mass of a material

  1. Aug 31, 2004 #1
    Hello,

    How can we find the mass of a material with density p is required to make a hollow spherical shell having inner radius r1 and outer radius r2 ?

    Thanks
     
  2. jcsd
  3. Aug 31, 2004 #2
    Find the volume of the shell by taking the volume of a sphere or radius r2 and subtract out the volume of a sphere of radius r1. Then multiply the mass density times the volume.

    Pete
     
  4. Aug 31, 2004 #3
    What is the volume of r1 and r2 ?!! there isn't any given numbers
     
  5. Aug 31, 2004 #4

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    Yes, there are! r1 and r2 are numbers.

    The volume of the hollow shell is [itex]\frac{4\pi}{3} (r_1^3-r_2^3)[/itex]. Now multiply by ρ to get the mass.
     
  6. Aug 31, 2004 #5
    Hint: The volume of a sphere of radius r is [itex]V = \frac{4}{3}\pi r^3[/itex].

    Pete
     
  7. Aug 31, 2004 #6
    you can think of r1 and r2 as just representations of numbers. It is a way of representing ANY number rather than one particular number. By doing this, if you have any sphere of any radius, you can just plug in the number you want to calculate in place of r1 and r2. This gives you a convienet equation that is applicable to any situation.
     
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