Question

Which type of motion of an object that moves at a fixed distance from a fixed point?
A) Periodic motion
B) Rectilinear motion
C) Circular motion
D) None of the above

Answer 1

Hint: The idea is to analyse different types of two dimensional motions. By doing so we can conclude what type of motion is letting an object move at a fixed distance from a fixed point. Consider examples like a car drifting in a circular track or a boy sitting in a merry-go-round.

Complete step by step answer:
In a motion with a fixed distance from a fixed point we can only imagine a circular trajectory for the object. However the path can be a full circle, half circle or even an arc.

The reason behind the above point is that, when an object is moving along the peripheral part/ circumference of a circle, its distance is always constant from the centre of the circle that is its radius $(r)$.

Examples of these types of motion include swinging of a stone tied to one end of a rope, rotating blades of a fan, satellite rotating at a fixed height from earth.

Let’s now consider the other options.
In periodic motion, the object oscillates between two fixed points, but gravity is constantly acting upon the bob/object, making its velocity decrease. This phenomenon also happens when in circular motion, the velocity of the object constantly decreases.

Again in periodic motion, the direction of the object continuously changes which changes its respective distance at the extremes of the oscillation path in every oscillation.
The rectilinear motion is the type of motion when the object moves in one direction only. If an object moves only in one direction, the distance will constantly increase from the starting point or it will change from any point on its path of action.
Thus we can conclude that in circular motion, to be more specific, in uniform circular motion (where speed/ velocity of the object is constant) or where the speed of the object continuously increases.

The correct answer is (C), circular motion.

Note: In some questions, the examiner might ask the difference between uniform and non-uniform circular motion. Keep in mind in any kind of uniform motion, the velocity of the object remains constant.