Question

An object travels North at `8 m/s` for `4 s` and then travels South at `6 m/s` for `7 s`. What are the object's average speed and velocity?

Answer 1

Average speed: `6 8/11 m/s`

Average velocity: `10/11 m/s " South"`

Explanation:

#{: (,ul("Distance"),color(white)("xxx"),ul("Displacement")), ("first 4 seconds",8m/sxx4s=32m,,8m/s N xx4s =32 m N), ("second 7 seconds",6m/sxx7s=42m,,6m/s Sxx7s=42 m S) :}#
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Total time: `4 s + 7 s=11s`

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Total distance: `=32 m + 42 m = 74m`

Average speed: `"distance"/"time"=(74 m)/(11 s)=6 8/11 m/s`

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

Total displacement: `32 m color(red)N +42 m S`
`color(white)("XXXXXXXXXXXXXXXXXX")=color(red)-32m color(red)S +42 m S`
`color(white)("XXXXXXXXXXXXXXXXXX")=10 m S`

Average velocity: `"displacement"/"time"= (10 mS)/(11s)=10/11 m/s S`