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Homework Help: Kinematics. Urgent yes or now answer!

  1. Feb 8, 2010 #1
    1. The problem statement, all variables and given/known data
    1. an object is thrown vertically up from a window that is 3.6m above the ground.
    Its initial speed is 2.8m/s.


    2. Relevant equations
    N/a


    3. The attempt at a solution

    Is the time the object takes to ascend equal to the amount of time it takes to descend?
     
  2. jcsd
  3. Feb 8, 2010 #2
    The acceleration of the oobject will be g down.
    now you can calculate the time spent to go up, because v0 = g*t
    the height travelled up: h=v0*t - 1/2*g*t^2
    now down: h+h0 = 1/2*g*t^2

    To look at it in a graphical way:
    draw a parabola upside down. x coordinate is the time, y is the height, the steepnes of the parabola is the speed. Move the parabola such that
    - it is raising at x=0 : the initial speed is positive
    - it is positive at x=0: initially it is in up in the window

    Now note whether the y distance of the top of the parabola form the origo (time spent up) is equivalent to the y distance from the top of the parabola to where it cuts the horizontal axis (time spent down).
     
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