AQA A Level Physics
AQA A Level Physics 3.11 Engineering Physics (Option C) Exam Questions
Free AQA A Level Physics exam questions for 3.11 Engineering Physics (Option C), with a mark scheme for every pack. Covers moment of inertia, torque, angular momentum, the first law of thermodynamics, p-V diagrams, engine cycles and heat pumps.
3.11 Engineering Physics (Option C) exam questions
2 question packs 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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About AQA A Level Physics 3.11 Engineering Physics (Option C)
Engineering Physics is optional topic 3.11 in AQA A Level Physics and is assessed in Section B of Paper 3 if your school chooses it. Section 3.11.1 Rotational dynamics is the rotational version of linear mechanics: moment of inertia, rotational kinetic energy, angular acceleration, torque, angular momentum and its conservation, and work and power in rotating systems such as flywheels. Section 3.11.2 Thermodynamics and engines covers the first law, isothermal and adiabatic changes, p-V diagrams, four-stroke petrol and diesel engine cycles, indicated and brake power, the second law, maximum efficiency, and refrigerators and heat pumps. It builds on mechanics from 3.4 and the ideal gas work in 3.6.2.
What you need to know
- 3.11.1 Moment of inertia I = sum of mr^2, which depends on how mass is distributed about the axis. Rotational kinetic energy = 1/2 I omega^2. Flywheels store energy and smooth out torque; know factors affecting their design.
- 3.11.1 Rotational motion Use the rotational equivalents of SUVAT with theta, omega and alpha. Torque T = I alpha, and torque = Fr for a force at radius r.
- 3.11.1 Angular momentum Angular momentum = I omega and is conserved when no external torque acts, as when an ice skater pulls in her arms. Angular impulse = T delta t = change in angular momentum. Work done W = T theta and power P = T omega.
- 3.11.2 First law and non-flow processes Q = delta U + W, where Q is energy supplied and W is work done by the gas. Isothermal: pV = constant; adiabatic: pV^gamma = constant; constant pressure: W = p delta V; constant volume: W = 0.
- 3.11.2 p-V diagrams and engines Work done in a cycle is the area enclosed on a p-V diagram. Compare theoretical and real indicator diagrams for four-stroke petrol and diesel engines. Indicated power = area of loop x cycles per second x number of cylinders; brake power = T omega; friction power is the difference.
- 3.11.2 Second law and heat pumps No heat engine can be 100 percent efficient. Efficiency = W/QH and maximum efficiency = (TH - TC)/TH. Coefficient of performance: refrigerator COP = QC/W, heat pump COP = QH/W, with ideal values from temperatures in kelvin.
Common mistakes in 3.11 Engineering Physics (Option C)
- Using the wrong sign convention in the first law. In AQA's form Q = delta U + W, W is the work done by the gas, so compression makes W negative.
- Thinking moment of inertia depends only on mass. It depends on how far the mass is from the axis, so two objects of equal mass can have very different values.
- Using temperatures in degrees Celsius for maximum efficiency or COP. Always convert to kelvin.
- Assuming an adiabatic process means constant temperature. In an adiabatic change Q = 0, so the temperature changes as work is done.
- Mixing up indicated power and brake power. Indicated power comes from the p-V loop; brake power is the useful output at the crankshaft.
Try three 3.11 Engineering Physics (Option C) exam-style questions
1. A flywheel of moment of inertia 0.25 kg m^2 accelerates uniformly from rest to 40 rad s-1 in 8.0 s. Calculate the torque applied and the kinetic energy gained. (3 marks)
Show the mark scheme answer
alpha = 40/8.0 = 5.0 rad s-2; T = I alpha = 0.25 x 5.0 = 1.25 N m; Ek = 1/2 x 0.25 x 40^2 = 200 J.
2. A heat engine works between 600 K and 300 K. Calculate its maximum theoretical efficiency and explain why a real engine is less efficient. (3 marks)
Show the mark scheme answer
Maximum efficiency = (600 - 300)/600 = 0.50 (50 percent); real engines lose energy to friction between moving parts; and the processes are not reversible, with heat losses and incomplete combustion.
3. Explain why an ice skater spins faster when she pulls her arms in. (3 marks)
Show the mark scheme answer
No external torque acts so angular momentum I omega is conserved; pulling the arms in moves mass closer to the axis so I decreases; so omega increases.
3.11 Engineering Physics (Option C) FAQs
What does AQA A Level Physics 3.11 Engineering Physics cover?
It covers rotational dynamics (moment of inertia, torque, angular momentum, rotational energy and power) and thermodynamics and engines (first and second laws, p-V diagrams, engine cycles, efficiency and heat pumps).
Which paper is the Engineering Physics option examined in?
If your school takes this option, it is assessed in Section B of Paper 3, after the practical skills section.
How do I learn the rotational dynamics equations quickly?
Pair each one with its linear version: mass with moment of inertia, force with torque, velocity with angular velocity, momentum with angular momentum and Fv with T omega. The SUVAT pattern is identical with angles in radians.
