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Yeah, I was wondering if it was possible ?

I have a function which have different variables depending on time, like:

$$\frac{d}{dt}mr^{2}\dot{\phi}$$

In this case both $r$, being a length, depends on time, and so does the time derived angle $\dot{\phi}$. I know this is an easy equation to solve in hand, but maybe sometime you get something a bit more difficult. So, can this be done in mathematica, and how ? :)

Hope you understand what I mean.

Thanks in advance.

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closed as off-topic by bobthechemist, Jens, m_goldberg, rm -rf Mar 19 at 5:13

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This question arises due to a simple mistake such as a trivial syntax error, incorrect capitalization, spelling mistake, or other typographical error and is unlikely to help any future visitors, or else it is easily found in the documentation." – bobthechemist, Jens, m_goldberg, rm -rf
If this question can be reworded to fit the rules in the help center, please edit the question.

    
D[m r[t]^2 D[ phi[t], t], t]? –  belisarius Mar 19 at 0:05
    
Ahhh, almost... I had just forgotten to put the variable, $t$, in brackets, and I was instead using parentheses. So now it is solved. Thank you :) –  Denver Dang Mar 19 at 0:12

1 Answer 1

up vote 2 down vote accepted
D[m r[t]^2 phi'[t], t]
(*
2 m r[t] phi'[t] r'[t] + m r[t]^2 phi''[t]
*)
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