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    jenimo123's Avatar
    jenimo123 Posts: 1, Reputation: 1
    New Member
     
    #1

    Jul 1, 2008, 12:17 PM
    Height formula
    This is my 4th time taking Physics. It is also the last class I need to be done with my degree. I can't understand it. I am getting very discouraged.

    Right now the question I have is I think a simple one I just can't think of it. How do you find the height of a table when all you have is a physics book fell off the table with a speed of 1.10m/s and it took 0.350s to hit the floor.
    eawoodall's Avatar
    eawoodall Posts: 230, Reputation: 5
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    #2

    Jul 2, 2008, 04:18 AM
    divide.

    how fast was it falling? How long did it take to fall?

    distance = rate times time.
    distance (miles) = rate (miles/hour) times time (hours).
    works same if you use meters and meters per second.

    after 4 years in physics you do not remember d=rt?

    Quote Originally Posted by jenimo123
    This is my 4th time taking Physics. It is also the last class I need to be done with my degree. I can't understand it. I am getting very discouraged.

    Right now the question I have is I think a simple one i just can't think of it. How do you find the height of a table when all you have is a physics book fell off the table with a speed of 1.10m/s and it took 0.350s to hit the floor.
    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
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    #3

    Jul 3, 2008, 03:59 AM
    Its simply proportionality

    As it says: 1.10 metre per second
    In one second, it makes 1.10 metre
    Therefore in 0.350 seconds, it makes : 1.10 * 0.350
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #4

    Jul 3, 2008, 05:26 AM
    An object that falls under gravity does not fall at a constant speed, but rather accelerates as it falls. When you say that the book fell with a speed of 1.10 m/s do you mean that it was given an initial downward "push" of 1.10 m/s, or do you mean that when the book hit the floor it was traveling at 1.10 m/s? If we assume the latter, then the distance an object travels is given by:



    In this problem you know that (the initial velocity) is 0, and (its final velocity) is 1.10 ms, and a = g = 9.8 m/s^2. So you simply plug and chug to find the distance .
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #5

    Jul 3, 2008, 12:53 PM
    Actually, the more I think about this... with the data that you are given there is a second way to solve this.

    The fact that the book hits the floor after 0.35s tells you that the distance it travelled is:



    The answer you get from this method does not agree with the solution from my previous post. Which means either (a) I am misunderstanding the question, or (b) the question was not properly written. So Jenimo - please repost with the problem as originally written - don't try to paraphrase it. Thanks.
    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
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    #6

    Jul 5, 2008, 02:45 AM
    Hey, you got a point there and I understand the difficulties now. I didn't pay attention to the acceleration due to gravity. Shame on me! Anyway, your second post seems more relevant to me.

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