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Homework Help: Determining the Height of a Building

  1. Sep 27, 2012 #1
    1. The problem statement, all variables and given/known data
    You are sitting by a window when someone on the roof drops a ball. The ball spends .30 seconds in front of the window (which is 1.50 meters tall.) The ball subsequently hits the sidewalk and bounces back up at the same speed. On its way up it passes by the window again taking .30 seconds in front of the window. If the ball spends 2.50 seconds underneath the window then how tall is the building?

    2. Relevant equations
    [itex]\Delta x = v_{0}t+(1/2)at^{2}[/itex]

    3. The attempt at a solution
    I have absolutely no idea how to approach this problem. I would appreciate any help.
  2. jcsd
  3. Sep 27, 2012 #2


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    2017 Award

    Staff: Mentor

    Hint: Try to find the distance d to the top first. After falling an unknown time t (without initial velocity), the ball has fallen a distance of d and reaches the top of the window. 0.3 seconds later the distance of the ball increased by 1.5 m. Try to express that with equations and solve them for d and t.
    Afterwards, try to find the total time the ball needs to reach the floor.

    You can assume that the building is on earth, so you know the acceleration.
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