Answer:
L=55.9m
Step-by-step explanation:
The equation for the period of a simple pendulum is:
![T=2\pi\sqrt{(L)/(g)}](https://img.qammunity.org/2021/formulas/physics/college/prcd1xpnvau5l1e0ccg16c8ear1152dunq.png)
In our case what we know is the period and the acceleration of gravity, and we need to know the length of the pendulum, so we can write:
![L=((T)/(2\pi))^2g](https://img.qammunity.org/2021/formulas/physics/college/go3ql33ynovexav3o1sksbjsdv6bjred8u.png)
Which for our values is:
![L=((15s)/(2\pi))^2(9.81m/s^2)=55.9m](https://img.qammunity.org/2021/formulas/physics/college/6g8xq1ht7ql0ycqj33o0k1nh0185sa4jl3.png)