A satellite of mass 850 kg moves at 7.5 x 103 m/s in a circular orbit of radius 7.0 x 106 m. Calculate the centripetal force on the satellite.
[3 marks]
Total for this question: 3
All equation deep-dives
Circular motion
Further mechanics
AQA 7408
In the data booklet
ORIGINAL
a = v2 / r = omega2 r and F = m v2 / r
Centripetal force is not an extra force; it is the resultant inward force supplied by real forces.
Board and spec code confirmed against AQA 7408 · registry checked 2026-07-11How this checking works
Know the equation
| Symbol | Quantity | Unit |
|---|---|---|
| a | centripetal acceleration | m/s2 |
| v | linear speed | m/s |
| r | radius of the circular path | m |
| omega | angular speed | rad/s |
| F | resultant centripetal force | N |
| m | mass | kg |
Rearrangements
- v = sqrt(a r)
- r = v2 / a
- v = sqrt(F r / m)
- omega = v / r = 2 pi / T
Apply it — mark your own working
Work each one out on paper first, then reveal the mark scheme and tick the marks you actually earned. That is exactly how you should mark past papers.
Q1
Do the calculation on paper first — then mark it.
Q2
The maximum resultant horizontal force on a 1200 kg car travelling around a level circular bend of radius 45 m is 6900 N. Calculate the maximum speed of the car.
[3 marks]
Total for this question: 3
Do the calculation on paper first — then mark it.
Where the marks get lost
- Writing 'centripetal force' as an additional force on a free-body diagram instead of identifying the real inward resultant.
- Using the diameter in place of the radius.
- Forgetting to square v, or squaring omega but not multiplying by r.
Exam tip: Start with a radial force equation such as gravity = m v2/r or friction = m v2/r. That shows which real force supplies the centripetal resultant.
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