$A$ particle moves along a circular path of radius $r$ with uniform speed $v$. The angle described by a particle in one second is

$A$ particle is moving along a circle such that it completes one revolution in $40 \, s$. In $2 \, \text{minutes} \, 20 \, s$, the ratio $\frac{|\text{displacement}|}{\text{distance}}$ is:

Assertion $(A)$: The speed of a body in uniform circular motion is constant.
Reason $(R)$: In uniform circular motion,the acceleration of the body is constant.

$A$ particle is moving in a circle with uniform speed. Its motion is

Assertion $(A)$ :- If a body is in a state of uniform circular motion,then its velocity and acceleration both are varying.
Reason $(R)$ :- If the magnitude of velocity is $v$ and the radius of uniform circular motion is $r$,then the magnitude of acceleration is $v^2/r$.

The length of the second's hand in a watch is $1 \, cm$. The change in velocity of its tip in $15 \, seconds$ is