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Gravitational field test with answers for A Level physics (free PDF download)

Quick answer: Newton's law of gravitation says two masses attract with force F = G m₁m₂/r². This Physics 11-12 test on gravitational field has 8 questions worth 20 marks, to do in 45 minutes: field strength definition, mars and satellite orbit. The mark scheme is on a separate page; free printable PDF.

Gravitational field test with answers for A Level physics (free PDF download)

This test lasts 45 minutes and is worth 20 marks. Calculators are allowed. Use G = 6.67 × 10⁻¹¹ N m² kg⁻² and give final answers with units and sensible significant figures. Measure all distances from the centre of the planet.

Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB D.1

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

Question 1 Field strength definition (2 marks)

Define gravitational field strength and state its direction.

Question 2 Mars (3 marks)

Mars has mass 6.42 × 10²³ kg and radius 3.39 × 10⁶ m. Use G = 6.67 × 10⁻¹¹ N m² kg⁻².
  1. Calculate the field strength at its surface. (2 marks)
  2. Calculate the weight of a 70 kg person on Mars. (1 mark)

Question 3 Satellite orbit (3 marks)

A satellite orbits the Earth at radius 7.2 × 10⁶ m. Use G M = 3.98 × 10¹⁴ m³/s².
  1. Calculate its orbital speed. (2 marks)
  2. Calculate its period in hours. (1 mark)

Question 4 Kepler’s third law (3 marks)

  1. State Kepler’s third law. (1 mark)
  2. Planet A orbits a star at a distance of 1.0 × 10¹¹ m with a period of 200 days. Planet B orbits the same star at 4.0 × 10¹¹ m. Calculate the period of planet B. (2 marks)

Question 5 Potential graph (3 marks)

The graph shows the potential V of the Earth.
Graph of gravitational potential in megajoules per kilogram against distance from the centre of the Earth in Earth radii; the curve starts at minus 62.5 at one radius and rises towards zero12340-20-40-60r (in Earth radii R)V (MJ/kg)surface
Gravitational potential of the Earth (V = −GM/r).
  1. Calculate V at the surface using G M = 3.98 × 10¹⁴ m³/s² and R = 6.37 × 10⁶ m. (1 mark)
  2. Use the graph to find the energy needed to lift 1.0 kg from the surface to r = 2R. (2 marks)

Question 6 Escape speed of Venus (3 marks)

Venus has mass 4.87 × 10²⁴ kg and radius 6.05 × 10⁶ m.
  1. Calculate the escape speed. (2 marks)
  2. Explain why the escape speed does not depend on the mass of the rocket. (1 mark)

Question 7 Weightlessness (2 marks)

Explain why astronauts in a spacecraft orbiting the Earth feel weightless although gravity still acts on them.

Question 8 Negative potential (1 mark)

State why gravitational potential is negative at a finite distance from a planet.

See the gravitational field test answers and mark scheme

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