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First law thermodynamics test with answers for AP Physics 2 (free PDF download)

Quick answer: The first law of thermodynamics states ΔU = Q + W: the internal energy of a gas changes by the heat added plus the work done on it. This AP Physics 2 test on first law thermodynamics has 8 questions worth 20 marks, to do in 45 minutes: first law with numbers, a two-step path and process types. The mark scheme is on a separate page; free printable PDF.

First law thermodynamics test with answers for AP Physics 2 (free PDF download)

This test covers the first law, PV diagrams, heat engines and entropy for AP Physics 2. Use ΔU = Q + W with W the work done on the gas, R = 8.31 J/(mol·K) and temperatures in kelvin. Show all working and give a short written reason wherever a question asks you to explain.

Level: AP Physics 2 (algebra-based) · Curriculum: AP P2 Unit 9

Time: 45 minutes · 8 questions · Total: 20 marks · Calculator allowed

Question 1 First law with numbers (3 marks)

A gas (0.10 mol, monatomic) absorbs 500 J of heat and expands, doing 200 J of work on its surroundings.
  1. State the values of Q and W (work done on the gas). (1 mark)
  2. Calculate ΔU. (1 mark)
  3. Calculate the temperature change. (1 mark)

Question 2 A two-step path (3 marks)

A pressure-volume path from A at 1 litre and 1.5 times 10 to the 5 pascals, to B at 3 litres and the same pressure, then down to C at 3 litres and 0.5 times 10 to the 5 pascalsV (L)p (10⁵ Pa)123412ABC
Path A to B to C.
A gas goes from A to B at constant pressure, then from B to C at constant volume.
  1. Calculate the work done by the gas from A to B. (1 mark)
  2. Show that the temperature at C equals the temperature at A. (1 mark)
  3. Calculate the net heat added from A to C. (1 mark)

Question 3 Process types (2 marks)

  1. In an isochoric process, state the work done and the relation between Q and ΔU. (1 mark)
  2. In an isothermal expansion of an ideal gas, explain where the energy for the work comes from. (1 mark)

Question 4 An engine claim (3 marks)

An engine absorbs 1200 J from a hot reservoir at 600 K and rejects 900 J to a cold reservoir at 300 K per cycle.
  1. Calculate the net work. (1 mark)
  2. Calculate the efficiency. (1 mark)
  3. Compare it with the Carnot efficiency and state whether the engine is possible. (1 mark)

Question 5 Maximum efficiency (2 marks)

A steam engine works between 450 K and 300 K.
  1. Calculate the maximum possible efficiency. (1 mark)
  2. State the minimum heat rejected for each 900 J absorbed. (1 mark)

Question 6 Entropy and heat flow (3 marks)

A heat flow of 900 J passes from a body at 450 K to a body at 300 K.
  1. Calculate the entropy change of each body. (2 marks)
  2. Explain why this process is allowed by the second law. (1 mark)

Question 7 Compressing a gas quickly (2 marks)

A gas in an insulated cylinder is compressed quickly.
  1. State the value of Q. (1 mark)
  2. Explain why the temperature of the gas rises. (1 mark)

Question 8 Engine or refrigerator? (2 marks)

A gas follows a closed cycle on a PV diagram.
  1. State the sign of the net work done on the gas when the loop is traced clockwise. (1 mark)
  2. State what kind of device the anticlockwise loop represents. (1 mark)

See the first law thermodynamics test answers and mark scheme

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