Motion in a straight line

Equations you need to know

v= Δx/Δt
a= (v-u) /t

Equations of motion

v =u + at
x= ut +1/2at2
v2=u2 + 2ax

Warning

You cannot use v=d/t to work out the velocity at a point if the object is accelerating

Δ means "change in"

Exam techniques

The material on this page will help you complete questions about things moving is a straight line. It is really important to check that the exam questions you are doing are about constant acceleration. If acceleration is not constant you will most likely be given graphs to analyse. How to analyse graphs will be reviewed on another page.

  • displacement= distance moved in a particular direction
  • velocity=change in displacement/time taken v=Δx/Δt
  • acceleration = change in velocity/time taken a=(v-u)/t

    • Displacement, velocity and acceleration can be postive or negative. In exam questions you must be clear which direction is postive and which is negative. If the exam question does not tell you this, you will have to decide for yourself. This is usually done by drawing an arrow next to the diagram with a plus sign (+) to indicate which direction you are taking as positive. The opposite direction is therefore negative.

    Intial velocity, final velocity and the rest

    If you see the words:

  • "stationary object/object at rest" it means the intial velocity (u) =0
  • "comes to rest " then the final velocity (v) =0

    • (c) The Undercover Physicist 2007.