Mastering Physics Solved! A child on a swing set swings back and forth with a period of 3.9 s and

A child on a swing set swings back and forth with a period of 3.9 s and an amplitude of 25º. Suppose that the motion is simple harmonic. What is the maximum speed of the child as she swings?

[@carolg981]

it is a quite long swing...3.7meters!