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HELP : Q12 of Ch. 02 of Fundamentals of Physics, Resnick

  1. Nov 22, 2009 #1
    1. The problem statement, all variables and given/known data
    A rapidly growing plant doubles in height each week. At the end of the 25th day, the plant reaches the height of a building. At what time was the plant one-fourth the height of the building?


    2. Relevant equations
    The problem is a part of chapter which deals only with linear kinematics. But I cannot understand, which part of 4, general kinematic equation, I must apply.

    3. The attempt at a solution
    It looks like a case of geometric progression, But I am not able to get a start
    Also, I tried to start it by actually creating a table where there are three columns.
    column 1 = no. of weeks
    column 2 = initial height
    column 3 = final height.

    After that I drew blank..............
     
  2. jcsd
  3. Nov 22, 2009 #2

    Mark44

    Staff: Mentor

    Work backwards from the time that the plant was the height of the building. When was it 1/2 the height of the building? When was it 1/4 the height of the building?

    This problem has nothing to do with kinematics.
     
  4. Nov 22, 2009 #3
    Hello Mark44,
    U r DAMN RIGHT!

    Once, I saw through your eyes, the prob was as clear as water

    On 25th day height is h
    On (25-7)= 18, height will be h/2
    On (18-7) = 11, height will be (h/2)/2 = h/4

    Beauty.......................

    ThnX...........................a LooooooooooooooooooooT
     
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