The period of a simple pendulum is given by:
[tex]T=2 \pi \sqrt{ \frac{L}{g} } [/tex]
where L is the length of the pendulum and g is the gravitational acceleration.
The pendulum in our problem makes one complete vibration in 0.333 s, so its period is T=0.333 s. Using this information, we can re-arrange the previous formula to find the length of the pendulum, L:
[tex]L= g \frac{T^2}{(2 \pi)^2}=(9.81 m/s^2) \frac{(0.333 s)^2}{(2 \pi)^2}=0.028 m [/tex]
