Question

An object travels North at `2 m/s` for `1 s` and then travels South at `4 m/s` for `9 s`. What are the object's average speed and velocity?

Answer 1

Average velocity = `"-"3.09..."ms"^-1 "south"`
Average speed = `3.45..."ms"^-1`

Explanation:

We will deal with speed first. Speed is how far something travels per second.

North - `"speed"*"time"="distance"; 2*1=2"m"`
South - `"speed"*"time"="distance"; 4*9=36"m"`

Total distance travelled = 2+36=38m
Total time = 2 + 9 = 11s

`"Average speed" = "total distamce"/"total time"`

`"Average speed" = 38/11 = 3.45..."ms"^-1`

Average velocity:

As average takes direction into accpunt as well, the north value will be taken as positive, and the south value as negative (opposite directions, think add and subtract).

North - `"velocity"*"time"="displacement"; 2*1=2"m"`
South - `"velocity"*"time"="displacement"; "-"4*9="-"36"m"`

Total displacement = 2-36=-34m
Total time = 2 + 9 = 11s

`"Average velocity" = "total displacement"/"total time"`

`"Average velocity" = "-"34/11 = -3.09..."ms"^-1`

As the value for average velocity is negative, and so is the inital south value, the average velocity is therefore `"-"3.09..."ms"^-1 "south"`.