Everything Science Grade 10

CHAPTER 21. MOTION IN ONE DIMENSION 21.3

If we have a displacement of∆~xand a time taken of∆t,~vavis then defined as:

average velocity (in m·s−^1 ) = change in position (in m)change in time (in s)

~vav = ∆∆~xt

Velocity can be positive or negative. A positive velocity points in the direction you chose
as positive in your coordinate system. A negative velocity points in the direction opposite
to the positive direction.

Average speed (symbolvav) is the distance travelled (D) divided by the time taken (∆t) for
the journey. Distance and time are scalars and therefore speed will also be a scalar. Speed
is calculated as follows:

average speed (in m·s−^1 )=distance (in m)time (in s)

vav=∆Dt

Example 1: Average speed and average velocity

QUESTION

James walks 2 km away from home in 30 minutes. He then turns around and walks

back home along the same path, also in 30 minutes. Calculate James’ average

speed and average velocity.

2 km

SOLUTION

Step 1:Identify what information is given and what is asked for

The question explicitly gives

• the distance and time out ( 2 km in 30 minutes)


• the distance and time back ( 2 km in 30 minutes)
  Step 2:Check that all units are SI units.

Physics: Mechanics 397