I am using a number of equations from a different paper. I am using those to derive another quantity.
Is it appropriate to just mention them one after another, without stating the assumptions behind the equations etc, since I am already citing the previous paper like
Equation 1 -- (1)
Equation 2 -- (2)
Equation 3 -- (3)
Equation 14 -- (14)
then state the physical meaning of each parameter in the above equations?
I tried looking at some example papers but couldn't find any in the particular journal I am writing for.
If it were 1 equation, it would be fine, but I am not sure how to handle so many equations.
Or should I just reference the main equation and state the rest in the supplemental section? I just read and it seems putting too many equations in a paper is not a good idea.
I'm not sure about the common practice in your field, but, as a mathematician, I feel that you have approached this thing from the wrong direction. You don't reuse equations from another paper; you reuse theorems. A theorem is a statement like
If A and B and C are true, then equations D and E hold, where the symbol F is defined as... and G is defined as...
Maybe the authors of the other paper did not formulate their result as a theorem, but it is one. It is a sloppy but common habit to throw the derivation of a result in front of the reader directly, instead of first stating it then proving it.
Another important point to note is that there are hypotheses and assumptions under which these equations hold; if you focus on equations rather than on the whole 'theorem' package, this information can very easily get lost.
So, my suggestion is: reformulate those results as theorems. It could be a single theorem with 14 separate equations as the thesis, if they are all related.
If the word theorem sounds too pompous, use proposition. If your result seems too simple to deserve this name, use lemma.