Retrieval Practice
Circular Motion — AQA A-Level Physics
Q1. Define a radian.
The angle subtended at the centre of a circle by an arc equal in length to the radius of the circle.
Q2. How many radians are in a full circle?
2 pi radians (approximately 6.28 rad).
Q3. Define angular speed and state its unit.
- The rate of change of angular displacement with respect to time.
- Measured in rad \(s^{-1}\).
Q4. Write three equivalent expressions for angular speed.
omega = delta theta / delta t = v/r = 2 pi f = 2 pi / T.
Q5. State the relationship between linear speed and angular speed.
- v = r omega.
- Linear speed equals radius times angular speed.
Q6. State three equivalent forms of centripetal acceleration.
a = \(v^{2}\) / r = r omega^2 = v omega.
Q7. What direction does centripetal acceleration act?
Towards the centre of the circular path, perpendicular to the velocity.
Q8. State three equivalent forms of centripetal force.
F = mv^2 / r = mr omega^2 = mv omega.
Q9. Is centripetal force a separate type of force? Explain.
- No.
- Centripetal force is the name for the resultant force when it acts towards the centre.
- It is always provided by a real force such as tension, friction, or gravity.
Q10. Explain why no work is done during uniform circular motion.
- The centripetal force is always perpendicular to the velocity.
- Since W = Fs cos theta and cos 90 = 0, no work is done.
- Kinetic energy stays constant.
Q11. Give three examples of centripetal force and name the real force providing it.
- Ball on string: tension.
- Car on roundabout: friction.
- Planet orbiting star: gravity.
Q12. How do you solve circular motion problems involving a real force?
Set the real force equal to the centripetal force expression (e.g. mg = mv^2/r for gravity) and solve for the unknown.