Uniform Circular Motion | Motion | Assessment | English | Grade 9

In a uniform circular motion which of the following physical quantity remains constant?

• Velocity

• Acceleration

• Speed

• All of the above

Answer explanation

Speed

A insect is moving in a circular path of radius 1m on the floor and completes 2 rounds at 4m/s. What is the time taken by insect to complete rounds?

• 1.57 seconds

• 3.14 seconds

• 6.28 seconds

• 12.56 seconds

Answer explanation

radius= 1 m, speed = 4 m/s Distance Covered by the insect = 2 × Circumference of the coin = 2× (2𝜋r) = 2 × (2 × 3.14 × 1) = 2 × 6.28 = 12. 56 m Time = Distance/speed = 12.56/ 4 = 3.14 s

Here in this image A, B and C are running in uniform circular motion in concentric circles, such that all of them complete one round at the same time. If the ratio of radius of A:B:C is 1/8:1/4:1/2, what will be the ratio of their speed?

• 1/8:1/4:1/2

• 0.1680671296

• 1/2:1/4:1/8

• None of the above

Answer explanation

Ratio of radius is 1/8:1/4:1/2 Ratio of distance is 1/8:1/4:1/2 Let time be T Ratio of speed = 1/8T:1/4T:1/2T

Which of the following statement is true for uniform circular motion?

• Displacement is zero when the half of the circle is covered.

• In a circular path direction changes at each point.

• The direction of acceleration and velocity is always same in a circular path.

• Magnitude of acceleration keeps changing in a circular path.

Answer explanation

When half of a circle is covered displacement is not zero, so option 1 is false. Direction of acceleration changes when an object slows down in a circular path, so option 3 is false. Direction of acceleration changes not the magnitude, so option 4 is true. Direction in a circular path changes at each point. Hence, option 2 is true

Diya rolls a car tyre from park to home.The tyre of the car with diameter 14 m rotates in uniform circular motion with a speed of 4m/s. If the total time taken by Diya to reach home is 11 minutes, what is distance between her home and the park in terms of the rotations of the wheel?

• 80 rotations

• 60 rotations

• 30 rotations

• None of the above

Answer explanation

Distance from park to home = distance covered by the tyre. Radius of the tyre= 14/2m = 7m Speed = 4 m/s Distance covered by tyre in one round = 2Πr = 2 × (22/7) × 7 = 44 m Time taken by tyre to complete one round = Distance/ speed = 44/4 = 11 seconds Total time taken to reach the house= 11 m = 660 s Total no. of rounds made by tyre = 660/11 = 60