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Simple pendulum, det the change of its period?

  1. Aug 17, 2008 #1
    Qn. A simple pendulum has a length of 3.00m. Det the change in it period if it is taken from a point where g=9.80ms2 to a higher elevation where the acceleration due to gravity decreases to 9.79ms2.

    i cannot seem to start the question and a bit unsure here...

    here is what i get...

    Formula to use:
    T = 2 pie sqrt L/g

    i dun think the answer is just (T=2pie sqrt L/9.80) - (T=2pie sqrt L/9.70) right?

    What i know, is that when the g start to reduce is at the point when it is starting going in the opposite direction, away from the equilibirium.(lowest point)

    Please help to get me..i am stuck here...
     
  2. jcsd
  3. Aug 17, 2008 #2

    Dick

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    Why do you think it isn't just the difference of the two periods? I think it is.
     
  4. Aug 17, 2008 #3
    isnt a the period pendulum is the same assuming that there isnt any damping?
     
  5. Aug 17, 2008 #4

    Dick

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    The period of the ideal pendulum just depends on L and g. In the real world, sure, it also depends on damping and the amplitude of the oscillation. But this looks like a pretty straightforward question. Just give the easy answer.
     
  6. Aug 17, 2008 #5
    Thanks for you opinion.....i also think that it is a straightforward answer..but no confidence....anyway...just try....to err is a learning process..

    thank you again..
     
  7. Aug 18, 2008 #6
    i did the equations...working.

    Change of period
    = (T=2pie sqrt 3/9.80) - (T=2pie sqrt 3/9.79)
    = 3.4768 - 3.4786
    = - 0.0018s

    is the answer logical?..
     
  8. Aug 18, 2008 #7

    Dick

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    Well, g only changes by a fraction of a percent, so the change in the period is small. And the period should go up as g goes down. So I'd say it's logical. But is it correct? You are subtracting two numbers of similar magnitude, so if you need to, you should worry about how many significant figures are correct. Especially since I don't seem to get exactly the same numbers as you. What are you using for pi?
     
  9. Aug 19, 2008 #8
  10. Aug 19, 2008 #9

    Dick

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    That accounts for the discrepancy.
     
  11. Aug 19, 2008 #10
    the answer is i got after re-correction = -0.001777s
     
  12. Aug 19, 2008 #11

    Dick

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    I get -0.001775...s, but I'll call that good enough.
     
  13. Aug 19, 2008 #12
    thanks....see how it goes...when i submit the answers..
     
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