Question

An object travels North at `6 m/s` for `3 s` and then travels South at `5 m/s` for `7 s`. What are the object's average speed and velocity?

Answer 1

Average speed is `5.3 m/s`.

Average velocity is `1.7 m/s " South"`.

Explanation:

`"Average speed" = "Distance"/"Time"`

The total distance is `6 m/s * 3s + 5m/s * 7s = 18 m + 35 m = 53m`.

The total time is `3s + 7s = 10s`.

Therefore the average speed is `(53m)/(10s) = 5.3 m/s`.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

`"Average velocity" = "Displacement"/"Time"`

The total displacement is :

`18m " North" + 35m " South" = 17m " South"`

The total time is `3s+7s = 10s`.

Therefore the average velocity is `(17m " South")/(10s) = 1.7 m/s " South"`

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Note that the average speed has no direction while the average velocity does (South).