Answer
$0.35$ Hz
Work Step by Step
We know that:
$$T=2\pi \sqrt{\frac{l}{g}}$$
We also know that:
$$f=\frac{1}{T}$$
Substituting the first equation into the second equation and simplifying:
$$f=\frac{1}{T}=\frac{1}{2\pi} \sqrt{\frac{g}{l}}$$ $$=\frac{1}{2\pi}$$
Now substituting the values and solving:
$$\sqrt{\frac{9.8m/s^2}{2.0m}}=0.35 Hz$$
