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Kinematics in 2d

  1. Sep 19, 2012 #1
    I have a problem with this question.
    An arrow is shot horizontally towards point O, which is at a distance of 20.0 m. It hits point P (right below point O) 0.10 s later. What is the distance OP (in metres)?
    What do i need to find? How would i know the time taken for the arrow to reach o?
  2. jcsd
  3. Sep 19, 2012 #2
    The distance to the target is a red herring; this is a question of kinematics in 1D: the vertical dimension.

    You know the arrow has been in free fall for 0.10s, and when something is in free-fall it accelerates downwards at 9.8 m/s^2. Since the arrow was shot horizontally, it's initial downward velocity is zero, and you can use

    x = 0.5*a*t^2 + v*t

    to find your distance.
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