Mechanics questions describe a physical situation and expect you to turn it into mathematics. Nearly every lost mark at the start of the course comes from skipping that translation step and reaching straight for a formula.
Always start with a diagram
Draw the object, mark every force acting on it with an arrow and a label, and mark the direction you are taking as positive. Weight acts downwards, normal reaction perpendicular to the surface, friction opposes motion, and tension acts along the string away from the object.
The modelling words matter
| Phrase in the question | What it tells you |
|---|---|
| Smooth | Friction is zero |
| Rough | Friction acts; you may need the coefficient |
| Light | The mass is negligible, so tension is the same throughout |
| Inextensible | Connected objects share the same speed and acceleration |
| Particle | Size is ignored; all forces act at one point |
A reliable method
- Diagram with all forces labelled.
- Choose a positive direction and state it.
- Resolve perpendicular and parallel to the motion.
- Apply F = ma in each direction, one equation at a time.
- Solve, then check the sign and size of the answer against the physical situation.
The final check catches most errors. A negative tension or an acceleration larger than gravity means something in the setup is wrong, not the arithmetic.