The formula to solve the length of a pendulum is:
[tex]L=( \frac{T}{2 \pi } ) ^{2} g[/tex]
Where:
L=length
T=period
g=9.8m/s^2 (This is constant)
Now just fill in what you know and solve for what you don't know. Based on the question, you know that the period is 3.89s.
[tex]L=( \frac{T}{2 \pi } ) ^{2} g[/tex]
[tex]L=( \frac{3.89s}{2 \pi } ) ^{2} 9.8m/s^{2}[/tex]
[tex]L=( 0.62s) ^{2}9.8m/s^{2}[/tex]
[tex]L=(0.3844s^{2})(9.8m/s^{2})[/tex]
[tex]L=3.76m [/tex]
The answer is then D.
