(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

http://img127.imageshack.us/img127/2695/coord2pq5gm6.jpg [Broken]

2. Relevant equations

[tex]\underline v = \dot r\;\underline e _r + r\dot \theta \;\underline e _\theta[/tex]

[tex]\underline a = \left( {\ddot r - r\dot \theta ^2 } \right)\underline e _r + \left( {r\ddot \theta + 2\dot r\dot \theta } \right)\underline e _\theta[/tex]

3. The attempt at a solution

Hi guys, been stuck on this question for a while now.

Here are the diagrams I made:

http://img183.imageshack.us/img183/9205/coord2pq5diag1rx9.jpg [Broken]

http://img359.imageshack.us/img359/3100/coord2pq5diag2xt7.jpg [Broken]

So from the second diagram:

[tex]\begin{array}{l}

\cos 15 = \frac{{ - \dot r}}{v} \\

\therefore \dot r = - v\cos 15 = - 50\cos 15 = - 48.296\;ms^{ - 1} \\

\end{array}[/tex]

then

[tex]\begin{array}{l}

\sin 15 = \frac{{ - r\dot \theta }}{v} \\

\therefore \dot \theta = \frac{{ - v\sin 15}}{r} = \frac{{ - 50\sin 15}}{{770}} = - 0.017\;\deg s^{ - 1} \\

\end{array}[/tex]

We are told in the question that the acceleration of P is zero, hence the components of acceleration must be zero:

[tex]\begin{array}{l}

0 = r\ddot \theta + 2\dot r\dot \theta \\

\Rightarrow r\ddot \theta = - 2\dot r\dot \theta \\

\therefore \ddot \theta = \frac{{ - 2\dot r\dot \theta }}{r} = \frac{{ - 2 \times - 48.296 \times - 0.017}}{{770}} = - 0.002\deg s^{ - 2} \\

\end{array}[/tex]

This isn't the right answer.

I think it could be do with my angles used because I thought angular velocity was meant to be measured in radians. All help will be greatly appreciated.

Thanks in advance.

Steven.

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# Homework Help: Polar Coordinates Problem

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