Edexcel IGCSE Physics revision

Astrophysics units questions

Choose the correct units for gravitational field strength and use force-per-unit-mass reasoning to explain them.

Edexcel IGCSE Physics Subtopic 8.a

Astrophysics units syllabus

Questions on astrophysics units can test recall, calculations, explanations, diagrams, data handling and practical skills. You should be able to:

8.1 use the following units: kilogram (kg), metre (m), metre/second (m/s), metre/second² (m/s²), newton (N), second (s), newton/kilogram (N/kg)

Write the unit symbol exactly and distinguish quantities that use similar-looking units.
Convert prefixes and compound units before substituting values into an equation.
Check that the unit of the final answer matches the quantity asked for.
Use the context of a diagram or calculation to reject units with the wrong dimensions.

These examples show how information in a diagram, graph or experimental context becomes part of a complete exam answer.

June 2011 · Paper 2P · Question 1(d)

Question 1

Gravitational field strength is measured in

A kg/N

B kg/N²

C N/kg

D N/kg²

C — N/kg

Gravitational field strength is the gravitational force per unit mass. Force is measured in newtons and mass in kilograms, so its unit is N/kg.

November 2023 · Paper 1P · Question 1(b)

Question 2

This question is about astrophysics.

Which of these is a correct unit for gravitational field strength, g?

□ A kilogram (kg)

□ B newton (N)

□ C newton kilogram (Nkg)

□ D newton per kilogram (N/kg)

D — newton per kilogram (N/kg).

Gravitational field strength is measured as force per unit mass. Force is measured in newtons and mass in kilograms, so the unit is N/kg.

Some candidates chose the newton alone. Remember that N is the unit of force; gravitational field strength is measured in N/kg.
Do not confuse kg, the unit of mass, with N/kg, the unit of gravitational field strength.

Build a focused practice set from this part of the Edexcel IGCSE Physics syllabus.