Most students who struggle with physics problems understand the ideas but lack a method. This guide gives you a repeatable process: read, draw, list, choose, solve symbolically, substitute and check, with worked examples from mechanics and electricity.
Physics problems reward process. Two students can know the same formulas, yet one gets full marks and the other gets stuck, because the first has a system for turning words into diagrams, diagrams into equations and equations into a checked answer. Markers also award method marks, so a clearly set-out solution earns credit even when the final number is wrong.
The method below works for introductory mechanics, electricity, waves and thermal physics, and it scales up to university courses. Practise it on easy problems until it is automatic; then it will carry you through hard ones.
| Step | What you do | Why it matters |
|---|---|---|
| 1. Read twice | Read the whole problem, then reread to extract information | Catches hidden data and what is actually asked |
| 2. Draw | Sketch the situation, then a free-body or circuit diagram | Turns words into physics |
| 3. List | Write knowns with units, and the unknown | Shows which equations can work |
| 4. Choose principles | Identify the governing law or equation | Avoids formula hunting |
| 5. Solve symbolically | Rearrange for the unknown before inserting numbers | Fewer errors, easier checking |
| 6. Substitute | Insert values in SI units and calculate | Consistent units give correct answers |
| 7. Check | Units, size, sign and limiting cases | Catches mistakes before the marker does |
On the first read, picture what is happening. On the second, underline every number and every phrase that carries hidden information.
Finally, identify exactly what the question asks for, including the unit and number of significant figures expected.
A diagram is not decoration. Most errors in mechanics come from a missing or misdirected force, and a diagram makes those visible.
Common free-body mistake: including forces the object exerts on other things. Newton's third-law pairs act on different objects, so only one of each pair belongs on any single free-body diagram.
Write every given value with its symbol and unit, converting to SI units immediately.
| Given as | Convert to SI |
|---|---|
| 72 km/h | 20 m/s (divide by 3.6) |
| 250 g | 0.250 kg |
| 15 cm | 0.15 m |
| 4.7 kΩ | 4700 Ω |
| 3 minutes | 180 s |
| 2.0 mm² | 2.0 × 10⁻⁶ m² |
Then write the unknown with a question mark. Your list now tells you which equations are usable: you need one that contains the unknown and otherwise only known quantities.
Ask which principle governs the situation before reaching for an equation.
| If the problem involves... | Consider... |
|---|---|
| Constant acceleration, distances and times | The kinematic (suvat) equations |
| Forces and acceleration | Newton's second law, ΣF = ma |
| Heights, speeds and no time information | Conservation of energy |
| Collisions or explosions | Conservation of momentum |
| Circular motion | Centripetal force, F = mv²/r |
| Circuits | Ohm's law and Kirchhoff's laws |
Energy methods are often faster than force methods when the path is complicated, because energy only depends on start and end states.
Send your questions. We provide fully worked, step-by-step solutions you can learn from.
Rearrange the equation for the unknown using symbols, and only then insert numbers. This keeps arithmetic errors out of the algebra, lets you check units on the formula itself, and makes your working easy for a marker to follow.
Problem: a 2.0 kg block slides down a 30° slope. The coefficient of kinetic friction is 0.20. Find its acceleration (g = 9.81 m/s²).
The mass cancelled in the symbolic answer, which you would miss if you substituted numbers early. That is also a useful physical insight: the acceleration does not depend on the block's mass.
Problem: a ball is released from rest and rolls without friction down a curved track, dropping 1.8 m vertically. Find its speed at the bottom, ignoring rotation.
Problem: a 12 V battery with negligible internal resistance is connected to a 4.0 Ω resistor in series with a parallel pair of 6.0 Ω resistors. Find the current from the battery.
For uncertainty in experimental values, see our uncertainty and error analysis guide.
Work problems before checking solutions, and when you get one wrong, identify which step failed: reading, diagram, principle, algebra or arithmetic. Keep a short list of the mistakes you make most often and check for them on every problem. Mix problem types rather than doing twenty of the same kind, because exams test whether you can recognise which principle applies, not only whether you can apply it.
Learn the core ones and understand where they come from. Many exams provide a formula sheet, so the skill being tested is choosing and applying the right principle.
Symbolic solutions reduce arithmetic errors, reveal quantities that cancel, let you check units and limiting cases, and make your method clear to markers.
Go back to your list of knowns and unknowns and your diagram. Ask what physical principle governs the situation: forces, energy, momentum or circuit laws. Then find the equation that links your knowns to your unknown.
Usually not. Most physics marking schemes award method marks for correct diagrams, equations and working, so clear presentation protects your marks.