Circular motion and angular velocityEdexcel A-Level Physics: Subtopic test

1. 1
   A fairground wheel of radius 12 m turns at a steady rate, completing one revolution every 40 s. A rider sits at the rim of the wheel.

   (a)

   What is the angular velocity of the wheel?

   [1 mark]

   • A0.025 rad s⁻¹
   • B6.3 rad s⁻¹
   • C2.5 × 10² rad s⁻¹
   • D0.16 rad s⁻¹

   (b)

   What is the speed of the rider?

   [1 mark]

   • A1.9 m s⁻¹
   • B0.30 m s⁻¹
   • C0.013 m s⁻¹
   • D75 m s⁻¹

   (c)

   Calculate the magnitude of the rider's centripetal acceleration.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A laboratory centrifuge rotor spins at a steady 6000 revolutions per minute. A sample tube holds its contents at a distance of 0.080 m from the axis of rotation.

   (a)

   What is the angular velocity of the rotor?

   [1 mark]

   • A1.0 × 10² rad s⁻¹
   • B3.8 × 10⁴ rad s⁻¹
   • C6.3 × 10² rad s⁻¹
   • D9.5 × 10² rad s⁻¹

   (b)

   Through what angle does the rotor turn in 0.025 s?

   [1 mark]

   • A2.5 rad
   • B16 rad
   • C900 rad
   • D4.0 × 10⁻⁵ rad

   (c)

   Calculate the speed of the contents of the tube.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A small body moves at constant speed v in a horizontal circle of radius r. In a short time Δt it turns through a small angle Δθ, so that its velocity changes from v₁ to v₂, both of magnitude v. The Moon is such a body to a good approximation: it orbits the Earth in a circle of radius 3.84 × 10⁸ m with a period of 27.3 days.

   (a)

   Show that the acceleration of the body is v²/r and state its direction.

   [3 marks]

   (b)

   Calculate the centripetal acceleration of the Moon.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A spin-dryer drum has a radius of 0.25 m and rotates at a steady 1200 revolutions per minute. Wet clothes are pressed against the inside of the drum wall.

   (a)

   Calculate, for the clothes at the drum wall, the angular velocity, the period of rotation, the speed and the centripetal acceleration.

   [6 marks]

   (b)

   A student says: 'The clothes move at a constant speed, so they have no acceleration.' She also says: 'Doubling the rotation rate of the drum would double the acceleration of the clothes.' Evaluate both statements.

   [6 marks]

   Total for question 4: 12 marks

End of questions