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Acceleration and cylindrical coordinates

  1. Feb 23, 2015 #1
    1. The problem statement, all variables and given/known data
    The question and my attempt are attached as pics 2015-02-23 14_46_15-Sheet#3CH11.pdf - Foxit Reader.png 2015-02-23 14_45_14-Sheet#3CH11.pdf - Foxit Reader.png
    2. Relevant equations


    3. The attempt at a solution
    I can't seem to find r¨ and θ¨. Assuming I already got r˙ and θ˙ (the answers are written after the question). The idea I tried was to get the acceleration equation in cylindrical coordinates,
    a=(r¨−rθ˙2)r^+(rθ¨+2θ˙r˙)θ^
    and the a in intrinsic coordinates (v˙t^+v2/ρn^) in our case I assumed that t^=i and n^=j and that assumption is correct because it got the r˙ right, then I got r^ and θ^ in terms of i and j and now we have 2 equations with 2 unknown. The problem is that it gets the answer wrong, I checked my numbers a trillion time, still cant get the answer, anyone have any idea what is wrong? 10428009_1594866114062921_7986662162992654878_n.jpg
     

    Attached Files:

  2. jcsd
  3. Feb 23, 2015 #2

    haruspex

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    I see nothing wrong with your method or working. Did you find ##\dot r## and ##\dot \theta## independently, or are you just using the numbers given? What numbers do you get for the second derivatives?
     
  4. Feb 23, 2015 #3
    i managed to get ##\dot r## and ##\dot \theta## but i didnt include it here, i am gonna use the given numbers for now, the question asks for second derivatives he gave me the answers but they dont match mine
     
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