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Calculate terminal velocity when given cross sectional area

  1. Feb 10, 2016 #1
    1. The problem statement, all variables and given/known data
    Two packages are dropped from an airplane. A parachute can increase the cross sectional area of each packages by a factor of 31. The parachute on package 1 fails to open, and the terminal speed of package 1 is 10 m/s. The parachute on package 2 opens.

    What is the terminal speed of package 2 in m/s?

    2. Relevant equations
    Unsure, considering the problem gave very few numbers to work with.
    R = ½CρAv2

    3. The attempt at a solution
    I figured since A (cross sectional area) is inversely proportional to vterminal2, that you would square package 1's vterminal (to get 100 m/s) and then divide by 31. I haven't submitted my answer yet so I'm not sure if it's right.
     
  2. jcsd
  3. Feb 10, 2016 #2

    haruspex

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    Have you left out a final step?
     
  4. Feb 10, 2016 #3
    Well, vterminal2 is proportional to 1/A, so 102 = 1/(A*31)
    Solving for A I then get 1/3100 m/s, which seems a little ridiculous.
    I submitted my answer (from my original solution--3.2 m/s) and it was wrong, so I know I'm missing something. I just can't seem to figure out what.
     
  5. Feb 10, 2016 #4

    haruspex

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    Here's a hint. The square of 10m/s is not 100m/s. What is it?
     
  6. Feb 10, 2016 #5
    Would it then be 100m2/s2? So I should take the square root of my answer?
     
  7. Feb 10, 2016 #6

    haruspex

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    Yes.
     
  8. Feb 10, 2016 #7
    Thank you so much! I don't know why I decided to neglect units for that problem.
     
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