## Chapter 1.2 - Uniform Circular Motion Exercise 17

Question 1
What do you mean by uniform circular motion?
Solution 1
When a particle moves with a constant speed in a circular path, its motion is said to be the uniform circular motion.
Question 2
Does the earth move around the sun with a uniform velocity?
Solution 2
No, the earth moves round the sun with a variable velocity. Since the direction of motion changes at each and every point the velocity becomes variable.

Question 3
What do you mean by a centrifugal force?
Solution 3
Centripetal force has a reaction force in accordance with the Newton's third law of motion. This oppositely directed force is called centrifugal force.
Question 4
Name the force acting away from the centre of circular path.
Solution 4
Centrifugal force acts away from the centre of circular path.

Question 5
A uniform circular motion is an accelerated motion. Justify it.
Solution 5
In uniform circular motion, a particle travels equal distances along the circular path in equal intervals of time, so the speed of particle is uniform. But the direction of motion of the particle changes at each point of circular path. Due to continuous change in direction of motion, the velocity of the particle is not uniform (or velocity is variable) i.e., the motion is accelerated.
Question 6
What is a centripetal force?
Solution 6
Centripetal force: The force acting on a body moving in a circular path. It acts along the radius of the circle and towards its centre.

Question 7
Name the SI unit of centripetal force.
Solution 7
The SI unit of centripetal force is newton (N).
Question 8
Is centrifugal force considered as the force of reaction of the centripetal force?
Solution 8
Centrifugal force is not a real force, but it is considered to describe (understand) a certain motion. It should not be considered as the force of reaction of centripetal force, although its magnitude is same as that of centripetal force.

Question 9
Explain the difference between a uniform linear motion and a uniform circular motion.
Solution 9
In uniform linear motion, the velocity is constant and acceleration is zero i.e., the uniform linear motion is an un-accelerated motion, while in a uniform circular motion the velocity is variable (although speed is uniform), so it is an accelerated motion.
Question 10
Name the force needed for circular motion. What is the direction of the force?
Solution 10
The force needed for circular motion is 'centripetal force'.
This force is always directed towards the centre of circle at each point of its path.

Question 11
Which of the following quantity remains constant in a uniform circular motion?
(a) force           (b) speed
(c) velocity        (d) acceleration
Solution 11
(b) speed
Question 12
Is the motion of moon around the earth in circular path an accelerated motion?
Solution 12
Yes, it is an accelerated motion.