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Kinematics in 2d, plane drops an object

  1. Jan 17, 2009 #1
    1. The problem statement, all variables and given/known data
    A certain airplane has a speed of 267.2 km/h and is diving at an angle of θ = 28.0° below the horizontal when the pilot releases a radar decoy (Fig. 4-37). The horizontal distance between the release point and the point where the decoy strikes the ground is d = 777 m. (a) How long is the decoy in the air? (b) How high was the release point?

    2. Relevant equations

    3. The attempt at a solution
    Okay, step one is to find the velocity in the x and y directions, here is my attempt:
    Vy=sin(-28)*267.2= -125.4428016
    Vx=cos(-28)*267.2= 235.9235968

    So we have the following knowns:

    Okay, cool, plenty of information. Let's solve for T first so we can find Dy afterwards:
    Dx=VxT + 1/2Ax(T^2)
    777=(235.9235968)(T) + (1/2)0(T^2)
    777=(235.9235968)(T) + 0

    Now at this point, I went on to solve for Dy, but we're gonna stop here for the following reason: when I submitted my answer for T to the wileyplus online system, it told me my answer was wrong. What did I do wrong? Everything seems to make sense. Please help!
  2. jcsd
  3. Jan 18, 2009 #2


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    Science Advisor

    The speed of the airplane is given in km/hr. You should check for consistency in your units ;)
  4. Jan 18, 2009 #3
    Ah jeez, totally overlooked that. Thanks for the help!
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