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Terminal velocity

  1. Dec 29, 2014 #1
    This is not a homework question. It is basic physics.

    The question in the book relates to terminal velocity. I think the answer in the book is incorrect. Please advise.

    Students are investigating how the area of a parachute affects the forces acting on it in freefall. Steel balls are attached to parachutes of varying sizes and then dropped from a fixed height, timing how long it takes to hit the ground.

    Then the book asks a question:

    Question: will the ball with the largest parachute will be travelling more quickly or more slowly than other balls travelling at terminal velocity?

    I think the answer should be slowly but the book says quickly.

    If you are the steel ball, wouldn't you rather have a large surface area parachute so that you fall slowly?
     
  2. jcsd
  3. Dec 29, 2014 #2

    CWatters

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    Are the balls all the same mass?
     
  4. Dec 29, 2014 #3

    jbriggs444

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    I agree with you. It is difficult to second-guess the book without better context.

    Given identical steel balls and different parachutes, the ball/parachute pair with the larger parachute should have the slower terminal velocity.

    The ball with the larger parachute will reach (or approach) its terminal velocity in less elapsed time. But the wording of the question seems to make this fact irrelevant.
     
  5. Dec 29, 2014 #4
    The balls are all the same size and mass. Only the parachute is changed
     
  6. Dec 29, 2014 #5

    FactChecker

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    The book author is wrong. If you are ever in a crashing airplane with him and there is only one parachute, you will be a lucky man.
     
  7. Dec 29, 2014 #6

    CWatters

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    I agree. book is wrong. Not the first time.
     
  8. Jan 11, 2015 #7
    I have fallen at Terminal Velocity many times and I always found that a parachute slowed me down, On the 1 occasion that I used a smaller parachute I believe that I fell faster than with the larger parachute and a lot slower than without the parachute. I would always prefer to hit the ground with an open parachute than without a parachute. Text books do not always have correct answers and/or information. Nothing beats doing your own experiment. (Typos edited)
     
  9. Jan 11, 2015 #8

    Orodruin

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    Is this the exact formulation gound in the book? I can also imagine the book asking which of the balls reach terminal velocity more quickly, but this is pure speculation as I do not have the book. See also post #3. If this is not the case, I agree with previous posters.
     
  10. Jan 12, 2015 #9
    I have re read the question as posted "Question: will the ball with the largest parachute will be travelling more quickly or more slowly than other balls travelling at terminal velocity? " and I realise that I don't understand the question. Perhaps it has not been types correctly.
     
  11. Jan 12, 2015 #10

    CWatters

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    The question seems ok to me.

    The ball with the largest parachute will be travelling more slowly than other balls (which have a small or no parachute) at terminal velocity.
     
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