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Homework Help: Kinematics 2d physics question help

  1. Nov 16, 2009 #1
    1. The problem statement, all variables and given/known data
    An Alaskan rescue plane drops a package of emergency rations to a stranded party of explorers. The plane is travelling horizontally at 100 m/s at a height of 50 m above the ground. What horizontal distance does the package travel before striking the ground? what is the veloicty of the package before it hits the ground?

    2. Relevant equations

    3. The attempt at a solution
    I found the x and y components but could not find time and further on. Any help is appreciated.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Nov 16, 2009 #2
    Let me ask you this:

    when the package initial leaves the plane, what is it's y-component of velocity? Also, as the package travels towards the ground, does the x-component vary at all?

    (side note: I am assume we are ignoring air resistance?)
  4. Nov 16, 2009 #3
    for the y component i got 44.8 and x component i got 89.4. I dont quite understand what you mean when you ask if the x component varies.

    and yes, ignore air resistance. I am in my first year of physics so Im sure the problems cant be too complex for you guys.
  5. Nov 16, 2009 #4


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    Homework Helper

    How did you get those values? Are you sure the y component is 44.8 when the package leaves the plane?

    Asking why the x component varies is the same as asking whether the package's horizontal speed changes. Does it?
  6. Nov 17, 2009 #5
    For the x component I used the equation: Vox=VoCOS(theta)

    Um I would guess that the horizontal speed doesn't change because velocity is constant in the x direction?

    sorry Im a complete newbie to physics and Im trying to study for a test that I am not completely ready for at the moment
  7. Nov 17, 2009 #6


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    How did you get V0 or theta?

    The package's horizontal speed is 100 m/s when it was dropped from the plane, so it follows that it must be 100 m/s throughout the package's flight.
  8. Nov 17, 2009 #7
    No, I dont know what you mean by the intial velocity vector. Ive never heard of it before :/.

    I think the package is travelling faster in the x direction because wouldnt it have an initial velocity of 100 m/s?
  9. Nov 17, 2009 #8
    I got theta by using tan^-1(50/100)

    did i at least do that right?
  10. Nov 17, 2009 #9
    well, think about that...

    theta is in radians (or degrees), 50[m]/100[m/s] give you units of seconds.
    Last edited: Nov 17, 2009
  11. Nov 17, 2009 #10
    Oh I see.

    So I guess my question is how do I find the x and y components correctly because I obviously did them wrong the first time. When I find the x and y components then I can find theta using inverse tan, correct?
  12. Nov 17, 2009 #11
    I am going to state some of what is known, think about these quantities/ideas.

    1) the x-component is constant because there isn't an acceleration in the x-direction.
    2) the initial y-component is zero because that is how the problem is defined.
    3) the package accelerates in the y-direction, this is due to gravity.

    How can we use some of this?

    (trigonometry isn't apart of this problem)
  13. Nov 17, 2009 #12
    Oh, I finally got it! those last three ideas really helped. i didn't realize that the initial y-component was supposed to be zero. Thanks a lot srmeier!
  14. Nov 17, 2009 #13
    My pleasure, I must sleep now ^^

    as you continue your journey remember these things (and think about why I would tell you them):
    1) the time in which it takes the object to travel form 50m to 0m in the y-direction is equal to the time in which the object travels horizontally in the x-direction.
    2) to solve a quadratic equation google: the quadratic formula. (because the initial y-velocity is zero you don't need this formula but it may come up on your test)
    3) to find a resultant vector given its components use the Pythagorean theorem.

    If these hints confuse you at first that is ok. Take things one step at a time.
    Last edited: Nov 17, 2009
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