Answer
$ y= -\dfrac{1}{4} \sin (\dfrac{2 \pi x}{5})$
Work Step by Step
Amplitude, $ A=-\dfrac{1}{4}$. It is negative because the object is "pulled down".
Now, period, $ P=\dfrac{2 \pi}{\omega}=5$
$\implies \omega=\dfrac{2 \pi}{5}$
Hence, the displacement of the particles after $ x $ seconds can be written as:
$ y= -\dfrac{1}{4} \sin (\dfrac{2 \pi x}{5})$
