Calculating Uniform Acceleration (AQA GCSE Physics)
Revision Note
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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
v2 = u2 + 2as
Where:
s = 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.
Answer:
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 × s
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, s = ? (this needs to be calculated)
Step 3: Substitute known quantities into the equation and simplify where possible
162 = 02 + (2 × 2.5 × s)
This can be simplified to:
256 = 5 × s
Step 4: Rearrange the equation to work out the distance travelled
s = 256 ÷ 5
s = 51.2 m
Examiner Tips and Tricks
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.
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