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Practice questions · Mass and weight

Kilograms, or newtons.

Six original Cambridge-style questions on the mass-versus-weight distinction, the W = mg calculation, weight on different worlds, and the unit error examiners see most often.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep the two apart

Mass in kg; weight in N, from W = mg.

01
[3 marks]

State the difference between the mass and the weight of an object, including the unit of each.

  • Mass is the amount of matter in the object, measured in kilograms (kg). ✓
  • Weight is the gravitational force on the object, measured in newtons (N). ✓
  • Mass is the same everywhere; weight depends on the gravitational field strength g. ✓
02
[2 marks]

Write the equation linking weight, mass and gravitational field strength, and state the unit of g.

  • W = m g (weight = mass × gravitational field strength). ✓
  • g is measured in newtons per kilogram (N/kg). ✓
03
Calculation
[2 marks]

A bag has a mass of 6.0 kg. Taking g = 9.8 N/kg, calculate its weight.

W = m g = 6.0 × 9.8

W = 59 N (58.8 N)

04
Analysis
[3 marks]

An astronaut travels from Earth to the Moon, where the gravitational field strength is smaller. State what happens to the astronaut's mass and to their weight, and explain why.

  • The mass stays the same, because the amount of matter does not change. ✓
  • The weight decreases. ✓
  • Weight is W = mg, and g is smaller on the Moon, so the weight is less. ✓
05
Calculation
[3 marks]

On Earth (g = 10 N/kg) an object has a weight of 500 N.

(a)Calculate its mass. (b)Calculate its weight on the Moon, where g = 1.6 N/kg.

(a) m = W ÷ g = 500 ÷ 10

m = 50 kg

(b) W = m g = 50 × 1.6

W = 80 N

06
Analysis
[2 marks]

A student writes: "The box has a weight of 12 kg." Identify the error and write a corrected statement, taking g = 10 N/kg.

  • The kilogram is a unit of mass, not weight; weight is a force, measured in newtons. ✓
  • Correct: the box has a mass of 12 kg and a weight of W = mg = 12 × 10 = 120 N. ✓