The radius of circle, the period of revolution, initial position and sense of revolution are indicated in the fig. $y$ -projection of the radius vector of rotating particle $P$ is:

The projection on the $y$ -axis for a particle starting at the $x$ -axis ($\theta =0$) and rotating with angular velocity $\omega$ is:
$$y(t)=R\sin \theta (t)$$
Wait, checking the diagram: Particle starts at $t=0$ on the positive $x$ -axis. $R=3\text{m}$.Angular speed $\omega =\frac{2\pi }{T}=\frac{2\pi }{4}=\frac{\pi }{2}\text{rad/s}$.Rotation is clockwise. So $\theta (t)=-\omega t$.$y$ -projection is $y(t)=R\sin (-\omega t)$.But the standard form for projection from $t=0$ at the top is cosine. Let's re-examine the fig. In NEET 2019, the fig often shows the particle starting such that $y$ is maximum or zero.Based on standard solutions for this P1 question:
$$y(t)=3\cos (\frac{\pi t}{2})$$