CIE A Level Physics
CIE A Level Physics Motion in a Circle Exam Questions
Free CIE A Level Physics exam questions for Motion in a Circle, with a mark scheme for every pack. Covers radians, angular displacement, angular speed, centripetal acceleration and centripetal force for uniform circular motion.
Motion in a Circle exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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A-Level Physics Flashcards for 2027 Onwards
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About CIE A Level Physics Motion in a Circle
Motion in a circle is Topic 12 of the Cambridge International AS & A Level Physics (9702) syllabus and the first of the A Level topics. It describes uniform circular motion using radians, angular displacement and angular speed, then explains why an object moving at constant speed in a circle is accelerating. You use a = rω^2 = v^2/r and F = mv^2/r. The topic underpins Gravitational fields, where gravity provides the centripetal force for orbits, and the motion of charged particles in magnetic fields. Examiners test unit conversions to rad s^-1 and identifying which force provides the centripetal force.
What you need to know
- Radians One radian is the angle subtended at the centre of a circle by an arc equal in length to the radius. 2π rad = 360°, and arc length s = rθ.
- Angular speed Angular speed ω = Δθ/Δt = 2π/T = 2πf, measured in rad s^-1. Linear speed v = rω.
- Centripetal acceleration An object moving in a circle at constant speed has an acceleration towards the centre, a = rω^2 = v^2/r, because its velocity direction is changing.
- Centripetal force The resultant force towards the centre is F = mrω^2 = mv^2/r. It is not an extra force; it is provided by tension, friction, gravity, a normal force or a magnetic force.
- Vertical circles For a mass on a string, tension is greatest at the bottom (T = mg + mv^2/r) and least at the top (T = mv^2/r - mg).
Common mistakes in Motion in a Circle
- Drawing 'centripetal force' as a separate force on a free-body diagram. It is the resultant of the real forces acting.
- Saying an object moving in a circle at constant speed has no acceleration. Its velocity changes direction, so it accelerates towards the centre.
- Leaving calculators in degree mode or using rev per minute as ω. Convert to rad s^-1 first.
- Describing a 'centrifugal force' pushing objects outwards. In the ground frame, objects tend to continue in a straight line.
- Using diameter instead of radius in v^2/r.
Try three Motion in a Circle exam-style questions
1. A wheel rotates at 1200 revolutions per minute. Calculate its angular speed. (2 marks)
Show the mark scheme answer
f = 1200/60 = 20 Hz; ω = 2πf = 2π × 20 = 126 rad s^-1.
2. A car of mass 1200 kg travels round a horizontal bend of radius 50 m at 15 m s^-1. Calculate the frictional force needed and state its direction. (3 marks)
Show the mark scheme answer
F = mv^2/r = 1200 × 15^2/50; F = 5400 N; directed towards the centre of the bend.
3. A 0.20 kg mass on a string of length 0.50 m moves in a vertical circle. At the lowest point its speed is 4.0 m s^-1. Calculate the tension in the string at this point. (3 marks)
Show the mark scheme answer
T - mg = mv^2/r; T = 0.20 × 9.81 + 0.20 × 4.0^2/0.50; T = 1.96 + 6.4 = 8.4 N.
Motion in a Circle FAQs
What does Cambridge AS & A Level Physics Motion in a circle cover?
It covers radians, angular displacement, angular speed, centripetal acceleration and centripetal force for objects in uniform circular motion.
Which paper is Motion in a circle examined in?
It is an A Level topic, so it is assessed in Paper 4 (A Level Structured Questions) and may provide a context in Paper 5.
What equations do I need for Motion in a circle?
Learn s = rθ, ω = 2π/T, v = rω, a = rω^2 = v^2/r and F = mrω^2 = mv^2/r.
