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Resultant force | IB Physics Practice | Physics Insight
IB Physics/A.2 Forces and Momentum/Question
EasyCalculate & apply2 marks3 minutes

Resultant force

A 4.0 kg box is pulled horizontally with a force of 18 N. A frictional force of 6.0 N acts in the opposite direction. Calculate the acceleration of the box.

Worked answer

Solution

  1. Step 1

    Resultant force: 18 - 6 = 12 N.

  2. Step 2

    Apply Newton’s second law: a = F / m.

  3. Step 3

    a = 12 / 4.0 = 3.0 m s⁻².

Final answer

3.0 m s⁻²

Common mistake

Using the applied force instead of the resultant force.

Concepts tested

  • Newton's second law
  • resultant force
  • friction

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