Forces of 6 N east and 8 N north act on an object. Find the size of the resultant force.
- The forces are at right angles.
- Resultant = √(6² + 8²) = √100 = 10 N.
Answer 10 N
GCSE Combined Science revision · Physics: forces, waves and magnetism
The idea
A single force can be resolved into two components at right angles to each other; two perpendicular forces can be combined into a resultant using a scale drawing or Pythagoras. An object moving in a circle at constant speed has a changing velocity because its direction changes, so it is accelerating. The speed of an accelerating object at a moment is the gradient of a tangent to its distance–time graph at that time.
- Draw forces to scale, tip to tail.
- Use Pythagoras for perpendicular forces.
- For speed at a moment, draw a tangent and find its gradient.
Watch out Constant speed in a circle still means acceleration, because velocity is a vector.
See it worked
Your turn
Forces of 5 N and 12 N act at right angles. What is the size of the resultant force, in newtons?
Why is a satellite in a circular orbit at constant speed accelerating?
A tangent to a distance–time curve passes through (2 s, 4 m) and (6 s, 24 m). What is the speed at that point, in m/s?
In past papers
4 official questions in 3 papers since 2018. The latest:
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