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Physics Projectile Word Problem -- Dropping packages from an airplane

  1. Apr 20, 2017 #1
    1. The problem statement, all variables and given/known data
    US Air Force C-17 Globemaster III aircraft were used to airdrop food to Afghan refugees in the early stages of the war against the Taliban in 2001. Calculate how far ahead of the drop zone a pilot would have needed to drop humanitarian aid packages if the delivery occurred at a speed of 263 m/s and an altitude of 3048 m to avoid enemy fire. Assume the packages were released from their containers immediately and neglect air resistance.

    2. Relevant equations
    t = 2H / g
    D = vt

    3. The attempt at a solution
    It takes 24.928 s for the package to reach the floor.
     
    Last edited: Apr 20, 2017
  2. jcsd
  3. Apr 20, 2017 #2

    haruspex

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    m/s? That's not a distance.
    Anyway, what do you mean by "distance the aircraft will have at this time"? The time you calculated is an elapsed time, not a point in time. Which point in time do you mean, and distance of the aircraft from where?
     
  4. Apr 20, 2017 #3
    *6556.064
    You are right its a distance based on an elapsed time, but I can't think of another way to find the position when the delivery occurred.
     
  5. Apr 20, 2017 #4
    You'd want to define your variables more clearly. Additionally, drawing a picture of what the problem asks for will always help in these types of problems.

    ##\vec v_0=\langle263,0\rangle \frac{m}{s}##
    ##h=3048 m##
     
  6. Apr 20, 2017 #5

    haruspex

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    It is the right thing to do, but I'm struggling to understand where your difficulty lies.
    In the context of the problem, what distance do you think this represents? How is that different from the distance you need to find?
     
  7. Apr 20, 2017 #6
    My difficulty lies, in what things I must find in order to get the initial position of the aircraft.
     
  8. Apr 20, 2017 #7

    haruspex

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    You don't need the exact position, just the distance from the drop zone.
    Please try to answer my other question. When you multiplied the horizontal speed of 263m/s by the descent time of 25 seconds, what distance did you think that would calculate? (And why did you later delete that from post #1?)
     
  9. Apr 20, 2017 #8
    1. that would calculate the range after delivery.
    2. I deleted it because I thought it was irrelevant to the solution.
     
  10. Apr 20, 2017 #9

    haruspex

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    By range, do you mean the horizontal travel of the parcel or of the aircraft?
    By "after delivery" do you mean from releasing the parcel or from landing of the parcel?
     
  11. Apr 20, 2017 #10
    1. The horizontal travel of the aircraft(but it can also apply to the parcel)
    2. the releasing of the parcel.
     
  12. Apr 20, 2017 #11

    haruspex

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    Ok. So if that is the horizontal travel of the parcel after it is released, how far ahead of the target does it need to be released?
     
  13. Apr 20, 2017 #12
    I've hit a wall, I don't know.
     
  14. Apr 20, 2017 #13

    haruspex

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    As Eclair_de_XII suggested, draw a diagram. Show the horizontal movement of the aircraft and the trajectory of the parcel. Mark the horizontal distance you calculated for the parcel after release. How far from the landing point is the release?
     
  15. Apr 20, 2017 #14
    Still can't get the answer, man I'm hopeless.
     
  16. Apr 20, 2017 #15

    haruspex

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    Suppose you are throwing rocks at a target on the ground some distance away. You can throw the rock 20m. How far from the target do you need to be when you throw?
     
  17. Apr 20, 2017 #16
    20 m
     
  18. Apr 20, 2017 #17

    haruspex

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    Right. So if the parcel continues on for 6556m after it is released, how far does the plane need to be in front of the target when releasing it?
     
  19. Apr 20, 2017 #18
    yes, it is 6556. Man what a bummer. I'm just devastaded because this is from a problem from a higher edition Phyics book, and ,as I was given an answer to "this" problem number, I started searching for the explanation. But it results that the questions are different, that's why I had such a hard time.
     
  20. Apr 20, 2017 #19

    haruspex

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    Not sure I follow. Are you saying you had reason to believe that answer wrong? If so, it would have helped if you had said that at the start.
     
  21. Apr 20, 2017 #20
    Basically. Man I'm sorry I wasted your time. Sorry for any inconsistencies with my English - second language.
     
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