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Motion question -

  1. Apr 19, 2009 #1
    Motion question - plz help

    1. The problem statement, all variables and given/known data
    A lift ascends with an upward acceleration of 1.5ms^(-2). At the instant its upward speed is 2.0ms^(-1), a loose bolt drops from the ceiling of the lift 3.0m from the floor. Calculate:
    (a) the time of flight of the bolt from ceiling to floor

    2. Relevant equations
    x(f) = x(i) + V(xi)t + (1/2)a(x)t^(2)

    final position = initial position + (initial velocity x time) + (0.5 x acceleration x time^(2))

    3. The attempt at a solution

    I attempted to solve this question by forming 2 equations and solving it, since when the bolt leaves the roof of the lift and by the time it reaches the floor of the lift, the lift would've moved up:

    BALL: x(f) = 0.5 x (-9.8) x (t^(2))

    LIFT: x(f) = 3 + 2t + (0.5 x 1.5x t^(2))

    answer: 0.73sec

    from the two above equations I could't get the right answer, so can someone plz tell me if I've formed the right equations? Thanks in advance....
  2. jcsd
  3. Apr 19, 2009 #2


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    Staff Emeritus
    Science Advisor

    Re: Motion question - plz help

    Look at the problem statment carefully.

    Initially, until the bolt becomes free, it is traveling with the lift, and it has the same upward initial velocity as the lift at the moment it becomes free.

    So rewrite BALL: x(f) = 0.5 x (-9.8) x (t^(2)) with the correct initial conditions

    Also realize that the initial position of the bolt is 3 m above the inital position of the floor.
  4. Apr 19, 2009 #3
    Re: Motion question - plz help

    Thanks for your reply, I never thought of that... Thanks again. :)
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