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IGCSE Pressure Question: How many balloons can be inflated?

  1. Jan 9, 2017 #1
    • New poster has been reminded to use the Homework Help Template when starting threads in the schoolwork forums
    Hi, very quick question... It does like this: Helium in a cylinder (Which will be used to inflate a number of balloons) has a volume of (6*10-3) cubic meters and a pressure of (2.75*106)Pa. The pressure in each of the helium balloons is (1.1*105)Pa, and the volume of each balloon (3*10^-3) cubic meters.The temperature of helium does not change. How many balloons were inflated?

    -How i solved it: Pressure * Volume = Constant so.... (6.0*10^-3)*(2.75*10^6)=V2*1.1*10^5... V2= 0.15m3... Now what i did here was divide the total volume of helium at 1.1*105 by the volume of helium in each balloon and so.....0.15/3*10-3.... My answer was 50 balloons.

    -Mark scheme has the following answer: (0.15-(6*10-3))/3*10-3... Can someone tell me where i went wrong?
    Thanks in advance.
     
  2. jcsd
  3. Jan 9, 2017 #2

    gneill

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    Do you expect the helium cylinder to be completely empty after all the balloons that can be inflated are inflated?
     
  4. Jan 10, 2017 #3
    If the volume of helium in the balloon is 0.15m3 at that pressure, then why not? We use all the 0.15m3 because 0.15 is divisible by 0.030 without any remainders...
     
  5. Jan 10, 2017 #4

    gneill

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    So the final pressure in the cylinder will be zero? A perfect vacuum? How does the last of the gas get moved to balloons where the pressure will be nonzero?
     
  6. Jan 11, 2017 #5
    Ah, now I understand.. Thank you very much!:biggrin:
     
  7. Jan 11, 2017 #6

    gneill

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    Staff: Mentor

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