The length L of a simple pendulum varies directly as the square of its period…

The length L of a simple pendulum varies directly as the square of its period T. If a pendulum with period 4 sec. is 64 cm long, find the length of pendulum whose period is 9 sec

Correct Answer: Option B

Explanation

(L propto T^2)

(L = kT^2)

(k = frac{L}{T^2})

when T = 4, L = 64.

(k = frac{64}{4^2} = 4)

(L = 4T^2)

when T = 9,

(L = 4 times 9^2 = 324cm)