Forces and Motion: The Toolkit That Solves Most Mechanics Questions
May 9, 2026 · 5 min · forces and motion · mechanics · physics A Level
Almost every mechanics question on a physics paper falls into one of five problem types. Recognise the type, reach for the right technique.
1. Single object on a flat surface
- Free body diagram with all forces
- Apply F = ma
- Solve
2. Inclined plane
- Resolve gravity along the slope (mg sin θ) and perpendicular to it (mg cos θ)
- Friction acts up the slope if the object slides down
- Apply F = ma along the slope
3. Pulley problems
- Two objects connected by a rope over a pulley
- Same magnitude of tension in the rope
- Same magnitude of acceleration (one up, the other down)
- Apply F = ma to each object separately, solve simultaneously
4. Circular motion
- Net force points toward the centre (centripetal)
- F = mv²/r
- Common cases: car on a banked road, satellite in orbit, ball on a string
5. Kinematics with constant acceleration
- Use SUVAT equations: s = ut + ½at², v² = u² + 2as, v = u + at
- Identify which two of s, u, v, a, t are given, pick the equation that uses them
The four-step routine that works for all five
- Draw the free body diagram (every force acting on every object)
- Identify the question type (which of the five above?)
- Write the equation
- Solve
Common pitfalls
- Missing a force on the diagram
- Wrong sign convention (pick a direction as positive and stick to it)
- Mixing up speed and velocity
- Using SUVAT when acceleration isn't constant