posted by Nicole .
A 21-kg child swings on a playground swing 3.4 m long. What is the period of her motion? If her brother, who weighs twice as much as she does,rides on the swing instead, what is the period of the motion?
I'm sure your text or class notes has the pendulum period (P) formula
P = 2 pi sqrt (L/g)
Note that it is independent of mass.