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Year 10 Science — Force and Newton's three laws

Add forces to find the net force, use F = ma and F = mg, say what Newton's three laws claim, and treat two connected objects as one system.

Name: ________________________

Before you start

Two everyday situations, and the forces acting in each.

12
  1. 1. A box being pushed along a floor — your push one way, friction the other
  2. 2. A ball floating on water — gravity down, buoyancy up

In each case two forces oppose each other. If they match, nothing changes; if they do not, the leftover is the net force.

  1. 1.A 0.1 kg bullet has a force of 2 N on it. What is its acceleration, in m/s²? Answer with a number.

  2. 2.A block has 14 N acting on it to the right and 6 N to the left. What is the magnitude of the net force, in N? Answer with a number.

  3. 3.Boxes of 3 kg and 5 kg are joined by a string and pulled along a frictionless floor by a force of 16 N. What is the acceleration of the pair, in m/s²? Answer with a number.

  4. 4.A net force of 12 N acts on a 3 kg trolley. What is its acceleration, in m/s²? Answer with a number.

  5. 5.Two boxes joined by a string are pulled to the right by one force. Tap the place where the force acting is internal to the system, and so drops out when the two boxes are treated as one object.

    Write the number of the part.

    1234

  6. 6.What is the gravitational force the Earth exerts on a 5 kg bag, in N? Answer with a number.

  7. 7.Put a rocket launch in order as Newton's third law explains it, starting from The engine produces gas.

    • That upward push is larger than the weight of the rocket
    • The engine produces gas
    • The net upward force lifts the rocket off
    • The gas pushes back on the rocket with an equal upward force
    • The engine expels the gas downwards

  8. 8.Match each of Newton's laws to what it claims.

    • Newton's first law
    • Newton's second law
    • Newton's third law
    • The acceleration is the net force divided by the mass
    • A force on one object is met by an equal and opposite force on the other
    • An object keeps its rest or its constant velocity until a net force acts

Answer key — Year 10 Science — Force and Newton's three laws

  1. 1. 20
  2. 2. 8
  3. 3. 2
  4. 4. 4
  5. 5. 2 — The string joining the two boxes
  6. 6. 49
  7. 7. 1. The engine produces gas 2. The engine expels the gas downwards 3. The gas pushes back on the rocket with an equal upward force 4. That upward push is larger than the weight of the rocket 5. The net upward force lifts the rocket off
  8. 8. Newton's first law → An object keeps its rest or its constant velocity until a net force acts; Newton's second law → The acceleration is the net force divided by the mass; Newton's third law → A force on one object is met by an equal and opposite force on the other