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Homework Help: Volumes of solids of revolution

  1. Mar 14, 2010 #1
    1. The problem statement, all variables and given/known data
    A circle with a radius of (a/2) is bored through the centre of a sphere of radius a. Find the volume of the remaining solid.

    2. Relevant equations

    3. The attempt at a solution
    I've been trying this for an hour now and I've been trying to find the remaining volume by finding the area of the cylinder bored + the little side bits on each side. I've just been getting really messy answers which aren't close to the actual answer.

    Urgently need a hand :)
  2. jcsd
  3. Mar 14, 2010 #2
    The easiest way to do this is in my opinion:
    Set the sphere in the center of an xyz-axis system with the axis of the cilinder the y-axis. (for example)
    Now consider just the first quadrant in the xy-axis system.
    You should know that you can make a function of the curve you see ( f(x)= sqrt( (a^2)/4 - x^2 ) )

    To find the volume of the cylinder inside the sphere you only have to rotate the function around the y-axis while integrating from 0 to a/4. Multiply by two and you have the total volume of the cylinder within the sphere.

    I'm sure you will be able to solve it now ;).
    Last edited: Mar 14, 2010
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