If l and m both are doubled then the period becomes √2*T
what is a simple pendulum?
It is the one which can be considered to be a point mass suspended from a string or rod of negligible mass.
A pendulum is a weight suspended from a pivot so that it can swing freely.
Here,
A certain frictionless simple pendulum having a length l and mass m
mass of pendulum = m
length of the pendulum = l
The period of simple pendulum is:

Where k is the constant.
Now the length and mass are doubled,
m' = 2m
l' = 2l



Hence,
If l and m both are doubled then the period becomes √2*T
Learn more about Simple Harmonic Motion here:
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