A frame of reference that is accelerated with respect to an inertial frame of reference is called a non-inertial frame of reference. A coordinate system fixed on a circular disc rotating about a fixed axis with a constant angular velocity $\omega$ is an example of a non-inertial fram of reference. The relationship between the force $\overrightarrow{F_{\text {rot }}}$ experienced by a particle of mass $m$ moving on the rotating disc and the force $\vec{F}_{i n}$ experienced by the particle in an inertial frame of reference is $$ \vec{F}_{\mathrm{rot}}=\vec{F}_{\mathrm{in}}+2 m\left(\vec{v}_{\mathrm{rot}}+\vec{\omega}\right)+m(\vec{\omega} \times \vec{r}) \times \vec{\omega}, $$ where $\vec{v}_{\text {rot }}$ is the velocity of the particle in the rotating frame of reference and $\vec{r}$ is the position vector of the particle with respect to the centre of the disc. Now consider a smooth slot along a diameter of a disc of radius R rotating counter-clockwise with a constant angular speed $\omega$ about its vertical axis through its center. We assign a coordinate system with the origin at the center of the disc, the $x$-axis along the slot, the $y$-axis perpendicular to the slot and the $z$-axis along the rotation axis $(\vec{\omega}=\omega \hat{k})$. A small block of mass $m$ is gently placed in the slot at $\vec{r}=(R / 2) \hat{i}$ at $t=0$ and is contained to move only along the slot.
The distance $r$ of the block at time $t$ is