Calculating Uniform Acceleration

The following equation of motion applies to objects moving with uniform (constant) acceleration:

(final speed)² − (initial speed)² = 2 × acceleration × distance travelled

$v^{2} - u^{2} = 2 \times a \times x$

Where:
- x = distance travelled in metres (m)
- u = initial speed in metres per second (m/s)
- v = final speed in metres per second (m/s)
- a = acceleration in metres per second squared (m/s²)

This equation is used to calculate quantities such as initial or final speed, acceleration, or distance travelled in cases where the time taken is not known

Worked example

A car accelerates steadily from rest at a rate of 2.5 m/s² up to a speed of 16 m/s.Calculate how far the car moves during this period of acceleration.

Step 1: Identify and write down the equation to use

- The question says that the car 'accelerates steadily' - so the equation for uniform acceleration can be used:

v² − u² = 2 × a × x

Step 2: List the known quantities

- Initial speed, u = 0 m/s (the car starts from rest)
- Final speed, v = 16 m/s
- Acceleration, a = 2.5 m/s²
- Distance, x = ? (this needs to be calculated)

Step 3: Substitute known quantities into the equation and simplify where possible

16² − 0² = (2 × 2.5 × x)

- This can be simplified to:

256 = 5 × x

Step 4: Rearrange the equation to work out the distance travelled

x = 256 ÷ 5

x = 51.2 m

Examiner Tip

Writing out your list of known quantities, and labelling the quantity you need to calculate, is really good exam technique. It helps you determine the correct equation to use, and sometimes examiners award credit for showing this working.

Calculating Uniform Acceleration (Edexcel GCSE Physics: Combined Science)

Revision Note