Physics · AQA 7408 · Option C · Topic 3.11

Engineering physics

Option: rotational dynamics and thermodynamics, including engines and heat pumps.

  • 12 sub-topics
  • Taught in Year 13
  • 104 practice questions
  • 12 animated lessons
Practice questions (104) Lessons Worksheets All AQA Physics topics

What the specification says

Every sub-topic AQA can examine in this topic, with its reference number from the official specification. The Y12 and Y13 tags show when each sub-topic is usually taught.

  1. 3.11.1 Rotational dynamics
  2. 3.11.1.1Concept of moment of inertiaY13
  3. 3.11.1.2Rotational kinetic energyY13
  4. 3.11.1.3Rotational motionY13
  5. 3.11.1.4Torque and angular accelerationY13
  6. 3.11.1.5Angular momentumY13
  7. 3.11.1.6Work and powerY13
  8. 3.11.2 Thermodynamics and engines
  9. 3.11.2.1First law of thermodynamicsY13
  10. 3.11.2.2Non-flow processesY13
  11. 3.11.2.3The p–V diagramY13
  12. 3.11.2.4Engine cyclesY13
  13. 3.11.2.5Second law and enginesY13
  14. 3.11.2.6Reversed heat enginesY13

Try 3 questions

Easy, medium and hard questions from this topic, each with a worked solutions and the mark for every step. All 104 questions in this topic, free, no account needed.

Engineering physics

Not needed for Year 12Easy

Angular momentum · Year 13 · 1 mark

  1. A flywheel of moment of inertia 1.5 kg m² spins at 12 rad s⁻¹. What is its angular momentum?
    (1)

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  1. Angular momentum = Iω. (½Iω² is the rotational kinetic energy.)D: 18.0 kg m2 s−118.0\ \mathrm{kg\,m^2\,s^{-1}}

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Engineering physics

Not needed for Year 12Medium

Moment of inertia · Year 13 · 3 marks

Masses of 2 kg are fixed at each end of a light rod of length 0.2 m, which rotates about its centre.
  1. (a)
    Calculate the moment of inertia of the system.
    (2)
  2. (b)
    Explain why a flywheel has most of its mass in the rim.
    (1)

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Part (a)2 marks

  1. I=∑mr2I = \sum mr^2
  2. I=0.0400 kg m2I = 0.0400\ \mathrm{kg\,m^2}

Part (b)1 mark

  1. I depends on r2r^2, so mass far from the axis gives a large moment of inertia for its mass.

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Engineering physics

Not needed for Year 12Hard

Conservation of angular momentum · Year 13 · 4 marks

A skater spins at 3.0 rad s⁻¹ with moment of inertia 4.0 kg m². She pulls her arms in, reducing her moment of inertia to 1.5 kg m².
  1. (a)
    Calculate her new angular velocity.
    (2)
  2. (b)
    Show that her rotational kinetic energy increases, and explain where the energy comes from.
    (2)

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Part (a)2 marks

  1. No external torque acts.I1ω1=I2ω2I_1\omega_1 = I_2\omega_2
  2. ω2\omega_2=8.00 rad s−1{}= 8.00\ \mathrm{rad\,s^{-1}}

Part (b)2 marks

  1. 18.0 J→48.0 J18.0\text{ J} \to 48.0\text{ J}
  2. Work done by her muscles pulling her arms in.

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