A rocket burns fuel and lifts off vertically from a launch pad, rising high above the Earth's surface. As the rocket rises, its weight decreases. State what is meant by weight and explain why the weight of the rocket decreases as it rises.

Cambridge International IGCSE Physics (0625) — 1.7 Energy, work and power · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

Weight is the gravitational force acting on an object, calculated as weight = mass × gravitational field strength.
The gravitational field strength (g) decreases as the distance from the Earth increases.
The mass of the rocket remains constant.
Therefore, as the rocket rises, g decreases while mass stays the same, so weight = mass × g decreases.

Examiner tips

  • Define weight and give the formula. Explain that g falls with altitude. State that mass is unchanged. Show the logical link to weight decreasing.

Common mistakes

  • Confusing mass with weight. Saying the rocket’s mass decreases. Ignoring that g decreases with height.

Mark scheme (4 marks)

  1. Weight is the gravitational force acting on an object with mass / weight = mass × gravitational field strength
  2. Gravitational field strength decreases as distance from Earth increases
  3. The mass of the rocket remains constant / does not change
  4. Since weight = mass × gravitational field strength, and g decreases (while mass is constant), weight decreases

Key terms in this question

weight

Related

More Energy, work and power questions

▶ Try answering this question with AI marking (free) →