Question

A pendulum takes 60 seconds to swing through 2 complete cycles.

Answer 1

A : 30 seconds
B: T = 2π Square root of√L/g,
C: how many back-and-forth swings there are in a second, measured in hertz. f = [√(4.9)]/6.28 = 2.21/6.28 = 0.353 Hz.

Answer 2

A. If nobody is messing with the pendulum, it's doing one complete cycle every 30 seconds.

B. That's exactly what "period" means, so A. and B. are the same number ... 30 seconds.

C. Frequency = 1/period.
1/30s = 0.0333.../s.
That's 0.0333... Hz.