Question

The mass in a pendulum clock completes one complete swing in 1.00 s . what is the length of the rod?

Answer 1

The period of oscillation of a pendulum is
$T=2 \pi \sqrt{ \frac{L}{g} }$
Where L is the length of the pendulum and $g=9.81 m/s^2$ the gravitational acceleration.
Re-arranging the formula and using T=1.0 s, we find the length of the pendulum:
$L= \frac{T^2g}{4 \pi^2}=0.25 m$