Question

a lift is ascending by acceleration g/3.what will be the time period of the simple pendulum suspended from its ceiling if its time period in stationery lift isT

Answer 1

You have to consider the elevator as an accelerated frame of reference.
This frame of reference will simulate a greater gravity g*.

First find g*, then use the standard formula for the time period of the simple pendulum to get T*.
Finally compare T* to the original T.

Answer 2

yes, time will be proportional to sqrt(L/a), where a = 2 g.

Answer 3

I would write g* = g + g/3