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EQUATIONS OF UNIFORMLY ACCELERATED MOTION
Many motion questions and problems can be solved using graphical methods, but we can also
use equations to calculate values we don’t know
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We can use them only for objects with uniform acceleration
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Key ideas about motion calculations
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If the motion is at constant speed or velocity, remember that you need to use only the
equations
S= vt and v =

𝑠
𝑡

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When you read a question, pick the key data and make a list as shown in the worded
examples
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Check that all the units are SI
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For a deceleration use a negative value of a in equation 2,4 and 5
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KEY FACT
In the equations
u = initial velocity or speed
v = finial velocity or speed
v – u = Δv = change of velocity
t or Δt = time interval
s = displacement or distance
a = acceleration
The equation
We start with the definition of acceleration:
1
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v = u + at
using average velocity = u + v ÷ 2
and s = vt, gives:
3
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s = ut + 1\2 at^2
5
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You do not need to know how to
derive them at this level
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Calculate her acceleration
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8 m\s^2

using equation 5
A train accelerates uniformly from rest at 0
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Calculate the finial velocity it reaches
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2 m\s^2
s = 1 km = 1000m
Note: use equation 5 for v when know s but not t
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2m\s^2)× 1000m
= 400 m^2 s^2
Finial velocity, v = 20m\s



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