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Drag Force and collision

  1. Oct 23, 2011 #1
    1. The problem statement, all variables and given/known data
    a ball makes a free-fall with zero initial
    velocity and an arrow with 25 m/s initial velocity is thrown to shoot
    this ball at the same time. The ball is initially h=38 m higher than the
    arrow.
    a) Assume no drag force then how long after does this collision occur?
    At what height below ball’s initial position does this collision occur?
    b) Assume a constant air drag force at any time instant, which is equal
    to Drag Force= 2.2 m where m is the mass of object. For this case,
    repeat part a). Take g=9.8 m/s2 for both parts of this and other
    questions.



    2. Relevant equations

    m.g-2,2m=m.a
    h=vo.t+1/2gt^2

    3. The attempt at a solution
    problem is in b part, i solved a.
    mg-2,2m=m.a
    a=7,6
    h=1/2at^2 =3,8t^2

    38-3,8t^2= 25.t -1/2.9,8.t^2
    there is an quadratic equation now and i think i should have used another formula, i'm not sure. I appreciate your help :)
     

    Attached Files:

  2. jcsd
  3. Oct 23, 2011 #2

    PhanthomJay

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    The quadratic is OK but you forgot to include the air resistance drag force on the arrow.
     
  4. Oct 23, 2011 #3
    i couldn't decide whether or not to include drag force on the arrow.because, in the question it says "Drag Force= 2.2 m where m is the mass of object" there is no information about the arrow
     
  5. Oct 23, 2011 #4

    PhanthomJay

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    Balls and arrows are both objects, as I see it..
     
  6. Oct 23, 2011 #5
    ok i tried that one too but i still have quadratic. how can i find t?
     
  7. Oct 23, 2011 #6

    PhanthomJay

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    Use quadratic equation, you know, if at^2 +bt + c = 0, then t = [-b +/- sq rt (b^2- 4ac)]/2a?
     
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