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The answer sheet for the worksheet Speed and energy on entry. Each answer comes with the reason, so it can be used to mark or to go over the questions with the class.

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KS3 · Ages 11 to 14 (Years 7 to 9)Answer sheet for teachers

Answers: Speed and energy on entry

  1. D: Less than a millimetreThe fusion crust is very thin, under a millimetre, because only the last film of molten rock freezes in place.
  2. C: The melted layer is swept off with its heatThe molten surface layer is constantly stripped off, and it takes its heat with it before that heat can travel inwards.
  3. C: They vibrate more strongly until the solid meltsHeating makes particles vibrate more strongly. When they vibrate strongly enough to break out of their fixed positions, the solid melts.
  4. A: Lower, as Earth's motion no longer adds to itHead on, Earth's orbital speed adds to the meteoroid's. Catching up from behind, Earth is moving away from it, so the speed between them is lower.
  5. B: The meteoroid squashing the air ahead of itAs the meteoroid ploughs into the air, it compresses the gas in front of it, and the compressed gas becomes extremely hot.
  6. False: the right answer is About 70 km/sHead on, the two speeds add: 40 + 30 = 70 km/s. Subtracting them would be the case if it were catching Earth up from behind.
  7. False: the right answer is Heat would have time to reach the insideThe inside stays cold partly because the heating lasts only seconds. Given hours, even slowly conducted heat would reach the interior.
  8. The kinetic energy lost goes to thermal stores, light and sound (accept any answer with the same meaning)Energy is never destroyed. The kinetic store shrinks, while the thermal stores of air and rock gain energy and light and sound carry energy away.
  9. Earth's gravity speeds up anything falling in (accept any answer with the same meaning)As a body falls towards Earth from far away, Earth's gravity speeds it up to at least about 11 km/s by the time it reaches the air.
  10. Freezing (accept any answer with the same meaning)A liquid turning into a solid is freezing, also called solidifying. Melting is the opposite change.

Task

Answers will vary. The task comes from the lesson: Draw an energy transfer diagram for a meteoroid entering the atmosphere. Start with the kinetic store, then show the transfers to the thermal store of the air and rock, and away by light and sound. Add a note explaining why the total energy is conserved even though the meteorite slows down.

Look for work that uses the key words correctly and gives a reason for each point.

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