Two pendulums begin to swing simultaneously. The first pendulum makes $11$ full oscillations when the other makes $9$. The ratio of the lengths of the two pendulums is

$A$ girl is swinging on a swing in the sitting position. What will be the effect on the time period of the swing if she stands up?

$A$ person measures a time period of a simple pendulum inside a stationary lift and finds it to be $T$. If the lift starts accelerating upwards with an acceleration $\left(\frac{g}{3}\right)$,the time period of the pendulum will be

At a place,the length of the oscillating simple pendulum is made $\frac{1}{4}$ times keeping the amplitude the same. Then,the total energy will be:

Two pendulums of length $121 \ cm$ and $100 \ cm$ start vibrating in phase. At some instant,the two are at their mean position in the same phase. The minimum number of vibrations of the shorter pendulum after which the two are again in phase at the mean position is:

What is a simple pendulum? Deduce an expression for the time period of a simple pendulum.