Solve Problems in GCSE Physics
Use these five steps to work through calculation questions clearly and check that your answer makes sense.
- Highlight the variables Identify what the question gives you and what you need to find. Write down each quantity with its symbol and value.
- Convert units Convert all values into the units required by the equation before substituting. For example, convert centimetres to metres or minutes to seconds where needed.
- Find the equation Choose an equation that contains the quantity you are finding and the values you know. Check that the units are consistent.
- Rearrange the equation with algebra If the unknown is not already the subject, rearrange the equation first. Do the same operation to both sides to keep it balanced.
- Substitute, calculate and give suitable significant figures Substitute the values with their units, calculate the result, then round to the appropriate number of significant figures. Follow any rounding instruction in the question; otherwise, use the precision of the given measurements.
Worked example
A cyclist travels 150 m in 12 s. Find the average speed.
1. Variables: distance d = 150 m, time t = 12 s; find speed v.
2. Units: Both values are already in metres and seconds.
3. Equation: v = d ÷ t.
4. Rearrange: v is already the subject.
5. Substitute and calculate: v = 150 m ÷ 12 s = 12.5 m/s. To 2 significant figures, the answer is 13 m/s.
1. Variables: distance d = 150 m, time t = 12 s; find speed v.
2. Units: Both values are already in metres and seconds.
3. Equation: v = d ÷ t.
4. Rearrange: v is already the subject.
5. Substitute and calculate: v = 150 m ÷ 12 s = 12.5 m/s. To 2 significant figures, the answer is 13 m/s.
Always include the unit in your final answer, and check that its size is physically reasonable.