# Physics Questions and Answers – Uniform Circular Motion

«
»

This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Uniform Circular Motion”.

1. The force that keeps the body moving in circular motion is _______
a) Centripetal force
b) Centrifugal force
c) Force of gravity
d) Reaction forces

Explanation: Centripetal force is responsible for keeping bodies moving in circular motion. The centripetal force is directly proportional to the square of the tangential velocity and inversely to the radius of circle.

2. The mathematical expression for centripetal force is ______
a) mv2/r
b) mv/r
c) v2/r
d) mv3/r

Explanation: The centripetal force is directly proportional to the square of the tangential velocity and inversely to the radius of circle. Hence, on calculating, we get the expression as mv2/r.

3. A body of mass 10 kg, is moving with a velocity of 5 m/s in a circle of radius 5 m, what is the centripetal acceleration of the body?
a) 5m/s2
b) 25m/s2
c) 0.5 m/s2
d) 50 m/s2

Explanation: The formula for centripetal force is mv2/r. Hence the centripetal acceleration is given by v2/r. Here, v = 5, r= 5. Hence, on solving we will get the centripetal acceleration as 5m/s2.

4. The centrifugal force always acts _____
a) Towards the center
b) Away from the center
c) In tangential direction
d) Outside of the plane of motion

Explanation: The centrifugal force always acts away from the center of the circle in which the body is moving. In contrast to this, the centripetal force always acts towards the center of the circle, keeping the body moving in the circle.

5. A ball is being rotated in a circle of radius 5 m with a constant tangential velocity of 20 m/s. A stone is also being rotated in a circle of radius 4 m with a constant tangential velocity of 16 m/s. Which one of the following choices is true about both the circular motions?
a) Both have same angular velocity
b) Both have different angular velocity
c) Angular velocity of ball > angular velocity of stone
d) Angular velocity of stone > angular velocity of ball

Explanation: Angular velocity = Tangential velocity/Radius. When we put in the values and calculate the angular velocities for each of the circular motions, we see that both the angular velocities are equal to each other and the value is 4 rad/s.

6. The angular velocity of a stone being rotated is 11 rad/s. What is the angular displacement covered in 0.5s?

Explanation: Angular velocity is the rate of change of angular displacement. Here the angular velocity is 11 rad/s. This implies that in one second the stone rotates by an angle of 11 rad. Hence in 0.5 s it will cover an angular displacement if 5.5 rad.

7. A body is moving in a vertical circular motion. Which one of the following forces does it not experience?
a) Force of gravity
b) Centripetal force
c) Normal reaction force
d) Centrifugal force

Explanation: A body moving in vertical circular motion experiences these four forces – centripetal force, centrifugal force, force of gravity, and resistance offered by the medium in which it is moving. Apart from these, it does not experience any other force in normal conditions.

8. A body of weight 20 N, mass 2 kg is moving in vertical circular motion with the help of a string of radius 1 m and with a velocity of 2 m/s. What is the tension in the string at the lowest point?
a) 28 N
b) 20 N
c) 8 N
d) 15 N

Explanation: At the lowest point, the body experiences centrifugal force and the weight in the same direction, opposite to the direction of tension in the string. Centrifugal force can be calculated as mv2/r = 8 N. Hence the tension = weight + centrifugal force = 28 N.

9. A body of weight 20 N, mass 2 kg is moving in vertical circular motion with the help of a string of radius 1 m and with a velocity of 5 m/s. What is the tension in the string at the highest point?
a) 30 N
b) 50 N
c) 20 N
d) 25 N

Explanation: At the highest point, the tension and the weight are in the same direction but the centrifugal force is in the opposite direction. Centrifugal force can be calculated as mv2/r = 50 N. Hence the tension = centrifugal force-weight = 30 N.

10. A body of weight 20 N, mass 2 kg is moving in vertical circular motion with the help of a string of radius 1 m and with a velocity of 5 m/s. What is the tension in the string when is horizontal?
a) 30 N
b) 50 N
c) 20 N
d) 25 N

Explanation: When the string is horizontal, the tension in the string and the centrifugal force are opposite to each other. Centrifugal force can be calculated as mv2/r = 50 N. Hence the tension = centrifugal force = 50 N.

11. Which one of the following devices acts on the principle of circular motion?
a) Centrifuge
b) Screw Gauge
c) Ruler
d) Vernier calipers

Explanation: The centrifuge utilizes the centrifugal force produced during circular motion. Centrifuge is commonly used to separate platelets from blood samples. It is an important equipment for studying blood. Other variations of centrifuge include devices like cream separator etc.

12. At which position in vertical circular motion is the tension in the string minimum?
a) At the highest position
b) At the lowest position
c) When the string is horizontal
d) At an angle of 35° from the horizontal 