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Free fall Question

  1. Feb 9, 2016 #1
    1. The problem statement, all variables and given/known data
    While parachuting, you dropped your sun glasses at a height of 1400m and it took 15 seconds for the glasses to fall onto the ground. What is your descend speed after you dropped your sun glasses?

    2. Relevant equations
    Y = VoT + 1/2at^2

    3. The attempt at a solution
    My thought process: The glasses must have the same velocity as me when I dropped them. Therefore, its initial velocity during the free fall is my descend speed.

    1400m = Vo(15s) + .5(-9.8m/s^2)(15s)^2
    Vo = 20 m/s

    The answer key says my descend speed is 9.8 m/s
     
  2. jcsd
  3. Feb 9, 2016 #2

    jbriggs444

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    A book that poses a problem involving parachuting without being cognizant of the fact that the terminal velocity of a pair of sunglasses is far, Far, FAR less than 100 meters per second should be discarded.
     
  4. Feb 9, 2016 #3
    This question was on a previous physics exam. Is there anyway for me to solve this with only knowing the basics of free fall?
     
  5. Feb 10, 2016 #4

    haruspex

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    I agree with jbriggs, but in an exam you just have to put up with it. Allowing for drag on the sunglasses would lead to an even larger answer, so I think your method was as intended by the question setter. You got a sign wrong in the first equation but appear to have corrected that, so I also agree with your answer.
     
  6. Feb 10, 2016 #5
    It's a typo in the answer key. They meant 19.8.
     
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