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Homework Help: Paint and weather balloon

  1. Oct 14, 2003 #1
    You launch a group of helium filled spherical weather balloons which have been painted with a thin layer of signal reflecting paint. the first balloon requires 2.75 liters of paint the second balloon you launch is bigger it's diameter is bigger by a factor of 2.75 how much paint will be needed for the second balloon. where do I start with this problem? is there a formula somewhere?
     
  2. jcsd
  3. Oct 14, 2003 #2
    the equation for the area of a sphere is
    a=4*pi*(r^2)
    suppose that a is the area of the first balloon
    Now to calculate tha area of the second balloon (a2) put
    a2=4*pi*((r*2.75)^2)
    =4*pi*(r^2)*7.56
    As you can see, the area of the second balloon is bigger than of the first by a factor of 7.56
    The quantity of paint you need to paint a balloon is proportional to the area of the balloon
     
  4. Oct 15, 2003 #3

    HallsofIvy

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    Science Advisor

    And that is proportional to the square of the diameter.
    Since the second balloon's diameter is 2.75 times as big, you will need (2.75)2= 7.5625 times as much paint, just as meteor said.
     
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