Answer:
C.√2T
Explanation:
The period of a new pendulum is expressed as;
T = 2π√L/g ..... 1
L is the length of the string
g is the acceleration due to gravity
If the length is doubled, the new length L2 = 2L
T2 = 2π√2L/g ....2
Divide equation 2 by 1;
T2/T = (2π√2L/g)/(2π√L/g)
T2/T = √2L/g * √g/L
T2/T = √2L/L
T2/T = √2
T2 = √2T
Hence its new period will be √2T
