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 200 J of heat and does 250 J of work pushing a piston. What is the change in its internal energy, Bo?

   -50 J
2. 2.

   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

3. 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

4. 3.

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

   • The model steam engine, since it does more work than the Stirling
   • The car engine, at 25%
   • The toy Stirling engine, since it is simplest
5. 4.

   Using the table, how much heat does the car engine give out as waste, Kira?

   • 750 J
   • 1250 J
   • 250 J
6. 5.

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

   • 10%
   • 20%
   • 90%
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 rises
   • It stays the same, since no heat flows
   • It falls
9. 8.

   A gas takes in 100 J of heat and does 100 J of work. What is the change in its internal energy, Pia?

   • 0 J
   • 100 J, since the heat counts and the work doesn't
   • 200 J
10. 9.

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

    • The cocoa warms up by taking heat from the room
    • Nothing, since both hold energy
    • The cocoa cools toward room temperature
11. 10.

    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
    • Work, from its electric motor
    • A colder room