Question

In a uniform circular motion, if the radius vector rotates by an angle of $\theta$, then its speed rotates by an angle.
(A) $\theta$
(B) $\dfrac{\theta }{2}$
(C) ${180^0}$
(D) It does not have a direction to be changed

Answer 1

Hint Scalar physical quantities only have magnitudes, and not direction. Vectors have both magnitude and direction. In a uniform circular motion, the speed is constant throughout the motion. But velocity keeps changing at every point of the trajectory.

Complete step-by-step solution
Speed is a scalar physical quantity, which only has magnitude but no direction. In the case of uniform circular motion, the speed is constant throughout the motion. It would be equal to the total arc length covered per unit time. If the radius vector turns by an angle $\theta$, the arc length would be equal to r $\theta$ .

Hence, the correct option is option D.

Note Many times we think that speed and velocity are the same things, but they are not. It is the velocity that changes its direction at every point of the trajectory of the circular motion. This question is a trick question to check the attention of the student. The only thing underlined here is that the speed is the scalar quantity.