The laws of thermodynamics and heat engines

Answer Key - Grade 11 Science Worksheet

Circle the best answer, or write your answer on the line.

1. 1.

   A gas in a model engine's cylinder takes in 300 J of heat and does 120 J of work pushing a piston. What is the change in its internal energy, Ari?

   180 J
2. 2.

   A gas in a model engine's cylinder takes in 200 J of heat and does 250 J of work pushing a piston. What is the change in its internal energy, Bo?

   -50 J
3. 3.

   A gas in a model engine's cylinder takes in 150 J of heat and does 60 J of work pushing a piston. What is the change in its internal energy, Esme?

   90 J

4. Read this first

   Engine tests (example data)

   Engine	Heat in (J)	Work out (J)
   toy Stirling engine	200	20
   model steam engine	500	40
   car engine	1000	250

5. 4.

   Using the table, which engine is the most efficient, Jun?

   • The car engine, at 25%
   • The model steam engine, since it does more work than the Stirling
   • The toy Stirling engine, since it is simplest
6. 5.

   Using the table, what is the toy Stirling engine's efficiency, Luz?

   • 90%
   • 10%
   • 20%
7. 6.

   In ΔU = Q − W, what does a positive W mean, Milo?

   • Work is done on the gas
   • The gas does work on its surroundings
   • Heat flows into the gas
8. 7.

   A piston squeezes a gas, doing work on it, with no heat flow. What happens to the gas's internal energy, Noah?

   • It stays the same, since no heat flows
   • It rises
   • It falls
9. 8.

   A cup of hot cocoa sits in a cool room. What happens by itself, Ren?

   • The cocoa cools toward room temperature
   • The cocoa warms up by taking heat from the room
   • Nothing, since both hold energy
10. 9.

    A refrigerator moves heat from its cold inside out into the warmer room. What does that need, Tala?

    • Nothing, since heat flows that way by itself
    • A colder room
    • Work, from its electric motor
11. 10.

    Why must a heat engine have a cold side, Zee?

    • To store the work it does
    • To stop the engine from moving
    • Heat must flow out for it to keep working