# Acceleration and cylindrical coordinates

1. Feb 23, 2015

### abdo799

1. The problem statement, all variables and given/known data
The question and my attempt are attached as pics
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?

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• ###### 10428009_1594866114062921_7986662162992654878_n.jpg
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2. Feb 23, 2015

### haruspex

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?

3. Feb 23, 2015

### abdo799

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