Question

An object travels North at `5 m/s` for `8 s` and then travels South at `5 m/s` for `2 s`. What are the object's average speed and velocity?

Answer 1

Speed is distance traveled per unit time, whereas velocity is displacement per unit time.

Recall,

`nu = (Deltax)/t" " bars = d/t`

We will assume an x-y coordinate system to be the reference frame, where south is negative and north is positive in direction.

Let's derive the magnitude of the displacement in each direction given your data,

`Deltax_"N" = (5"m")/"s" * 8.0"s" approx 40"m"`
`Deltax_"S" = (5"m")/"s" * 2.0"s" approx 10"m"`

`Sigmad = 50"m"`, and
`Sigmat = 10"s"`

Hence,

`bars = (50"m")/(10"s") = (5"m")/"s"`, and

`nu = (40"m" - 10"m")/(10"s") = (3"m")/"s"`

are the average speed and velocities of the moving body.