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Homework Help: Tricky pendulum question

  1. Sep 20, 2009 #1
    1. The problem statement, all variables and given/known data

    hey sorry about this again but i'm having trouble with some questions :eek::

    http://www.physics.ox.ac.uk/Admissions/undergraduate/admissions_test/tests07.pdf [Broken]

    3. The attempt at a solution

    page 6) okay well the bit i'm not sure about here is that L(cm) seeing as it is the distance to the COM i substituted r/2 for the uniform rod and r for the one with the bob giving me;


    i guess it makes sense because it would go to my simplified versions when simplified

    then with the 24 hour one it's really tricky...

    i worked out how much a time period would be to give a difference of 1 day + 1 second, then I worked out what the difference in r would be which gave me;

    0.469K for brass and
    7.429K for invar, do you think that's reasonable?

    note i used the formula for a pendulum of negligible mass and a mass on the end.


    page 10) question 6, I literally have no idea, i KNOW that it's a silly rule or something reguarding a equilateral triangle in a circle or some rule you can draw on however i'm just blank on this one, any pointers in the right direction would be great...

    thanks again!
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Sep 20, 2009 #2
    bump, i know it's alot to ask but some help would be great
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