Lesson 3.03h

3.03h Newton's third law and contact forces Quiz: OCR Maths, Unit 18

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.03h, Newton's third law and contact forces: 20 multiple choice questions for the OCR Maths (H240), Unit 18: Forces and Newton's Laws, written with Revision Ninja.

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The 20 questions

  1. According to Newton's third law, every action force has what type of reaction force?

    • Equal and parallel
    • Greater and opposite
    • Smaller and perpendicular
    • Equal and opposite

  2. On what do the action and reaction forces of a Newton's third law pair act?

    • Two different bodies
    • Three linked bodies
    • A single particle
    • The same body

  3. In what direction does the normal reaction force act relative to a contact surface?

    • Vertically downwards
    • Parallel to surface
    • Perpendicular to surface
    • At forty-five degrees

  4. In mechanics modelling, what does describing a contact surface as smooth imply?

    • Zero mass
    • Zero weight
    • Zero friction
    • Zero normal reaction

  5. A body rests on a horizontal plane with no other vertical forces. How does R compare to W?

    • R is larger
    • Equal magnitude
    • R is zero
    • W is larger

  6. What is the value of the normal reaction force when contact with a surface is lost?

    • Maximum
    • Greater than zero
    • Equal to weight
    • Zero

  7. When can a system of connected objects be modelled as a single particle?

    • Zero total mass
    • Constant speed
    • No external forces
    • No relative motion

  8. A book of mass 1.5 kg rests on a horizontal table with no other vertical forces. Taking g = 9.8 m s^-2, what is the normal reaction on the book?

    • 9.8 N
    • 1.5 N
    • 14.7 N
    • 15.3 N

  9. A man of mass 80 kg stands on the floor of a lift accelerating upward at 1 m s^-2, with g = 9.8 m s^-2. What is the normal reaction from the floor on the man?

    • 80 N
    • 720 N
    • 784 N
    • 864 N

  10. A block of mass 5 kg rests on a smooth horizontal table and is pushed vertically downward by a force of 10 N. Taking g = 9.8 m s^-2, what is the normal reaction?

    • 10 N
    • 39 N
    • 49 N
    • 59 N

  11. A block of mass 4 kg rests on a smooth horizontal table and is pulled horizontally by a force of 10 N. Taking g = 9.8 m s^-2, what is the normal reaction?

    • 10 N
    • 14.2 N
    • 39.2 N
    • 49 N

  12. A person of mass 60 kg stands on horizontal ground. The ground pushes up on the person with a force of 588 N, taking g = 9.8 m s^-2. What is the reaction force that the person exerts on the ground?

    • 60 N downward
    • 588 N downward
    • 9.8 N upward
    • 588 N upward

  13. A car exerts a 12 kN force on a lorry. What force does the lorry exert on the car?

    • 0 kN
    • 12 kN opposite
    • 12 kN forward
    • 24 kN opposite

  14. A block A of mass 3 kg rests on a block B of mass 2 kg which rests on a smooth horizontal table. Taking g = 9.8 m s^-2, what is the normal reaction between A and B?

    • 9.8 N
    • 19.6 N
    • 29.4 N
    • 49 N

  15. A block of mass 2 kg rests on a smooth horizontal table. It is pulled vertically upward by a force P. Taking g = 9.8 m s^-2, what value of P makes the normal reaction zero, so that contact is lost?

    • 29.4 N
    • 9.8 N
    • 19.6 N
    • 2 N

  16. Blocks A of mass 4 kg and B of mass 6 kg are in contact on a smooth horizontal table. A horizontal force of 20 N pushes A, which pushes B. What is the magnitude of the contact force between A and B?

    • 12 N
    • 8 N
    • 20 N
    • 10 N

  17. What is the Newton's third law reaction force to the weight of a book?

    • Friction from table
    • Downward contact force
    • Book pulling Earth
    • Table's normal reaction

  18. A block of mass 5 kg rests on a smooth horizontal table. A string attached to it pulls upward at 30 degrees above the horizontal with tension 20 N. Taking g = 9.8 m s^-2, what is the normal reaction?

    • 44 N
    • 59 N
    • 39 N
    • 49 N

  19. Two particles of masses 2 kg and 3 kg are in contact on a smooth horizontal surface. A horizontal force of 15 N pushes the 2 kg particle, which then pushes the 3 kg particle. What is the contact force on the 3 kg particle?

    • 5 N
    • 15 N
    • 6 N
    • 9 N

  20. What is the contact force on a body inside a freely falling lift?

    • Zero
    • Double mg
    • Mass m
    • Weight mg

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