We know that when a particle is moving along a curve in a plane,

then the transverse component of velocity is \( {v}_{r}=\dot{r} \).

[To know the derivation of the radial component of velocity (CLICK HERE) ]

Since the particle moves in such a way that the distance from the origin of the particle remains constant, this means that \( r=constant \).

Therefore, \( \dot{r}=\displaystyle{\frac{dr}{dt}}=0 \).

So in this case, the radial component of the velocity of the particle is zero.