What is the effect on the frequency of oscillation if a girl stands suddenly on a swing?

QUESTION:

A girl is swinging seated in a swing. What is the effect on the frequency of oscillation if she stands?

ANSWER:

If the girl sitting on swing stands suddenly, the frequency of oscillation will increase (time period decreases) because in the standing position, the location of center of mass of the system of swing and girl shifts upwards. Due to it, the effective length of the swing decreases.

As frequency f α 1/ √l , l - effective length of the pendulum(swing).

As effective length l of the swing decreases, f increases.