A2 12 Circular Motion Basics

The time taken for one complete revolution is called the _____.

• Period

• Angular velocity

• Frequency

A particle completes 6.0 revolutions in 4.0 s. The angular velocity, in rad/s, is ______.

• 1.5 rad/s

• 9.4 rad/s

• 24 rad/s

• 150 rad/s

Answer explanation

Angular velocity,

ω = (6 x 2π)/4

The drum of a washing machine rotates with an angular velocity of 8.5 rad/s.

The time to complete 10 revolutions is ___.

• 0.85 s

• 1.3 s

• 3.7 s

• 7.4 s

Answer explanation

Time for 10 cycles = (10 x 2π)/ 8.5

Which arrow represents the speed of the bowling ball?

• A

• B

• C

• D

Answer explanation

The speed (aka linear velocity) is always tangent to the circular path! This path is straight because of inertia.

Which arrow represents the acceleration of the ball?

• A

• B

• C

• D

Answer explanation

Centripetal acceleration always points towards the centre of the circular path!

The diagram shows an object travelling at a constant speed in a circular path.

Which labelled arrow represents the centripetal force acting on the object?

• W

• X

• Y

• Z

Answer explanation

The resultant force pointing TOWARDS THE CENTRE of the circle is called "centripetal force".

A child is sitting on the right-hand side in a car, facing the direction of travel.

The car goes round a bend to the left. The child remains in the same position within the car.

The student experiences ______.

• a force to the left and a force to the right.

• a resultant force to the left.

• a resultant force to the right.

• no resultant force.

An electric fan rotates at 800 rpm. The distance from the tip of a blade of the fan to the centre is 30.0 cm.

Calculate the linear speed of the tip of a blade in m/s. (3.s.f).

• 0.14

• 4.00

• 24.2

• 25.1

Answer explanation

First, ω= (800x2π)/60 = 83.8 rad/s.

Then, v = rω = (30x83.8) = 25.1

A racing car of mass 1200 kg travels at 0.63 rad/s around a bend of radius 50 m.

The force on the car necessary for this motion is ___.

• 2.4 × 10⁴ N away from the centre of the circle.

• 2.4 × 10⁴ N towards the centre of the circle.

• 3.8 × 10⁴ N away from the centre of the circle.

• 3.8 × 10⁴ N towards from the centre of the circle.

Answer explanation

Use F = mrω²