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An ant on the edge of a disc

  1. Sep 27, 2012 #1
    1. The problem statement, all variables and given/known data An ant positioned on the very edge of a Beatles record that is 14.80 cm in radius revolves through an angle of 70.0o as the disk turns. What is the ant's path length?
    What is the magnitude of the ant's displacement?

    2. Relevant equations L=Rtheta

    3. The attempt at a solution
    i was able to find the path length to 0.181 m and thats right but i cant find the displacement which seems like it should be easy...i used c^2=a^2+b^2 but that didnt work then i used costheta that didnt work so i used s=rtheta and that didnt work so .....please help, thanks
  2. jcsd
  3. Sep 27, 2012 #2


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    Gold Member
    2016 Award

    This gives you an isosceles triangle with two known sides and the angle between them also known ... how hard can it be ? Divide it into two right triangles and go from there.
  4. Sep 28, 2012 #3
    i did that and CAPA is still rejecting my answer...
  5. Sep 28, 2012 #4


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    Staff: Mentor

    Why don't you write out, in full, one of your attempts so that we can see what might be going wrong?
  6. Sep 29, 2012 #5
    i did radius times tan35 equal the opposite leg then multiply by two ......207
  7. Sep 29, 2012 #6


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    Staff: Mentor

    Ah, but I don't see that expression being correct. The radius is not the adjacent leg of the triangle.
  8. Oct 1, 2012 #7
    ic i found my mistake, thanks!
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