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Homework Help: Projectile Motion - Distance between Packages

  1. Mar 3, 2012 #1
    1. The problem statement, all variables and given/known data
    A package of supplies is dropped from a plane and one second later a second package is dropped. Neglecting air resistance, the distance between the falling packages will:

    A) Be constant
    B) decrease
    C) increase
    D) depend on their weight

    2. Relevant equations
    Sv=1/2 av t^2

    3. The attempt at a solution
    Well I thought it would be constant but my teacher informed me it was C. He didn't explain why though. I'm assuming the planes speed is constant, which means both package will be subject to the same horizontal component of velocity. However the first package would have already fallen (4.9 meters) downwards due to gravitational acceleration. The second one would then be released and would be subject to the same forces. (As horizontal component of velocity would remain constant)

    So I don't see how they would have an increasing distance.

    My idea was,

    Sv=1/2(9.8)(1)^2 = 4.9

    Sv=1/2(9.8)(2)^2 = 19.6

    Sv=1/2(9.8)(3)^2 = 44.1

    Therefore, when package 1 is at 4.9, package 2 is at 0 (displacement). [difference 4.9 m]
    When package 1, is at 19.6, package 2 is at 4.9. [difference of 14.7m]

    etc and its increasing.

    I think this is the right answer. How can I explain this in a sentence using physics terms. Its a multiple choice question so no calculations were needed even though I did some.

  2. jcsd
  3. Mar 3, 2012 #2
    Which direction, x-or -y is the question referring?
  4. Mar 3, 2012 #3
    Both x and y. However as the horizontal component won't change, we can just use the vertical component correct?

    As both have the same trajectory.
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