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    limexx_35's Avatar
    limexx_35 Posts: 1, Reputation: 1
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    #1

    Oct 16, 2005, 03:01 PM
    Can anyone help me with this problem?( science
    A brick falls from the top of a building and strikes the ground with a velocity of 19.6m/s. How long does the brick fall?
    SSchultz0956's Avatar
    SSchultz0956 Posts: 121, Reputation: 10
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    #2

    Oct 17, 2005, 09:23 AM
    Are you asking how long as in time or how long as in distance? Since Velosity = displacement/time elapsed does the problem give more information than the velocity? If so you could say time = V/displacement and Displacement = V* time
    Borewyrm's Avatar
    Borewyrm Posts: 65, Reputation: 2
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    #3

    Jan 23, 2006, 07:52 PM
    ... acceleration due to gravity 9.81 meters per second squared... Its been ten years since high school but that is it no?
    dmatos's Avatar
    dmatos Posts: 204, Reputation: 26
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    #4

    Jan 23, 2006, 08:16 PM
    Based on the number given in the question, I'd assume acceleration due to gravity is 9.8m/s^2.

    The equation for velocity in terms of constant acceleration is:

    v(t) = v0 + a*t

    Where v0 is the initial velocity, a is the acceleration, and t is the time. You can now solve for time given v(t) = 19.6, v0 = 0, and a = 9.8.

    If the question is asking "how long" in terms of total distance fallen (which I don't think it is), start by solving for the time, then use the formula

    d = v0*t + a*t^2/2, which you get by integrating v(t) = v0 + a*t.
    rudi_in's Avatar
    rudi_in Posts: 251, Reputation: 45
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    #5

    Jan 24, 2006, 07:15 PM
    Thank you for posting your question to the Ask Me Help Desk!

    I would go about solving this problem in the following manner...

    acceleration = (final velocity - initial velocity) / time

    Our acceleration in this problem is the acceleration due to gravity which is 9.8 m/s/s

    Our final velocity is 19.6 m/s/s as indicated by the problem.

    Our initial velocity is 0 m/s/s which is derived from the fact that before it began to fall off the building, it was not moving.

    We can then solve for time.

    9.8 = (19.6 - 0) / t

    9.8 = 19.6/t

    multiply both sides by t

    9.8t = 19.6

    divide both sides by 9.8

    t = 2

    The brick fell for 2 seconds.

    I hope that this was helpful.
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