How to find the period of a simple pendulum in an elevator going up with an acceleration?

How to find the period of a simple pendulum in an elevator going up with an acceleration of $a$.

Don't just say, $T=2 \pi$ $\sqrt{ \frac l {g+a}}$

I want to know how the above equation is formed.

• What do you think? – CuriousOne Jun 2 '15 at 2:59
• I downvoted this because the answer is on this site and one 10 second search found it. – user81619 Jun 2 '15 at 3:11
• I searched you know but couldn't find anything helpful – jessij Jun 2 '15 at 3:14