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Center of Mass and Mass Moment of Inertia

  1. Dec 2, 2009 #1
    1. The problem statement, all variables and given/known data
    Using masses, springs a stop watch and ruler, determine the location of the center of mass and mass moment of inertia about an axis passing through the center of mass of a bicycle crank.



    3. The attempt at a solution

    I've been staring at this problem for a while now and I have no idea where to start. Any help would be much appreciated. I have included a link with what the bike crank looks like.

    http://s429.photobucket.com/albums/qq12/ACE_99_photo/" [Broken]
     
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Dec 2, 2009 #2

    tiny-tim

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    Hi ACE_99! :smile:

    How about using conservation of energy …

    suspend the crank so that it hits the spring. :wink:
     
  4. Dec 2, 2009 #3

    jambaugh

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    To start how would you actually use what you are given to find the mass of the object?

    Is there more than one way?

    Given we often can treat objects as point masses concentrated at their center of mass for some problems can you think of any position dependent effect of mass or weight?

    As to moment of inertia... what behavior depends on the moment of inertia (you also have a stop watch).

    Given the spring (of which presumably you know the spring constants) you have the ability to invoke various types of (note plural types) oscillatory motion the period of which you can time. What oscillatory motion depends on one of the quantities you wish to find?
     
  5. Dec 2, 2009 #4
    Thanks for replies guys. With your method tiny-tim, I'm still not sure how I could use this to find what I'm looking for. Could you elaborate a bit?

    Reading through your questions got my mind thinking but I'm still stumped. Any more helpful ideas?
     
  6. Dec 2, 2009 #5

    tiny-tim

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    Come off it!

    You have to do some work! :rolleyes:

    How would you use conservation of energy (and include the moment of inertia) if the crank hit the spring?
     
  7. Dec 3, 2009 #6

    jambaugh

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    Go through your physics text and look for formulas which depend on the specific quantity you want to find. Can you think of a way to exemplify one of those formulas?
     
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