Question

A boy is whirling a stone tied at one end such that the stone is in uniform circular motion. Which of the following statements is correct?

(A) The velocity of stone at A is equal to the velocity of stone B.
(B) The speed of stone at A is equal to the speed of stone at B.
(C) The centripetal force is radially outward in the string.
(D) All of the above statements are correct.

Answer 1

Hint: This type of question can be solved by analyzing the options given. By dealing with options carefully we will get to know which a proper answer statement is. Firstly, we will see what is the quantity that changes in uniform circular motion. Then, we will see the forces that maintain uniform circular motion and their properties. By doing this we will finally reach the conclusion.

Complete step by step answer:
We already know that in uniform circular motion, velocity being a vector quantity changes constantly as the direction keeps changing whereas speed remains constant in uniform circular motion.
Now, talking about centripetal force, it acts inwards towards the centre to balance the centrifugal force acting outwards from the center.
As velocity changes in uniform circular motion so option (A) is incorrect. Now, as centripetal force is acting inwards so, option (C) is incorrect. As (B), (C) are incorrect so, (D) is also incorrect.

So, the correct answer is “Option B”.

Note: Uniform circular motion- It is defined as the motion of the object in a circle at constant speed. It is a periodic motion with definite frequency and period. The condition of uniform circular motion is, the net force and acceleration is directed inwards. If centrifugal force is absent then, the object cannot move in a circular motion. The example of uniform circular motion can be the movement of blades in a windmill. In circular motion, the direction of velocity at a point is always along a tangent.