Question

justify the statement 'the time period of a pendulem can be changed'

Answer 1

For a simple pendulum, where the pendulum is itself considered of negligible mass which moves with a minimal amplitude, the time period is given by the formula
T = 2(pi)*(sqrt(L/g))
where T is the time period, L is the length of the pendulum, and g is the gravitational constant.  By lengthening the pendulum, the weight at the end must travel a longer distance as it swings, which means more time is required for it to complete a given period.

Answer 2

if we change the length of the string ,the time period of pendulum may vary