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Homework Help: Kinematics Problem.

  1. Sep 24, 2004 #1
    hi guyes, I was wondering if someone could help me with a problem I had on a quiz. The question hes been puzzeling me for some time now.

    A ball is thrown upward in an open roof elevator travelling at 10m/s(elevator speed). The balls speed is 20m/s. How much time does it take for the ball to reach the same point it was thrown at?
  2. jcsd
  3. Sep 24, 2004 #2


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    Homework Helper

    You could use galilean transformations to solve this one, the 10m/s of the elevator must be relative to a inertial frame observer, as the 20m/s. Find the speed relative to the elevator, to simplify calculations.
  4. Sep 24, 2004 #3

    Doc Al

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    Staff: Mentor

    Is the elevator rising or falling?
    I assume that's the ball's speed with respect to the earth/elevator shaft.
    I assume you mean same point with respect to the elevator car?

    Find the position of the elevator car as a function of time. (Constant speed.)
    Find the position of the ball as a function of time. (Constant acceleration.)

    Set them equal and solve for the time.
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