An object travels North at # 7# #ms^-1# for #6# #s# and then travels South at # 3# # ms^-1# for # 7# # s#. What are the object's average speed and velocity?

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Answer 1 · 2017-06-20T21:45:09

The average speed is #4.9# #ms^-1#

The average velocity is #1.6# #ms^-1# North.

First step: find the distances traveled in each direction. We could also draw a diagram to the picture is clear in our heads.

We know #v=d/t# and can rearrange to give #d=vt#.

For the movement North, #d=vt=7xx6=42# #m#.

For the movement South, #d=vt=3xx7=21# #m#.

Over all, then, the distance traveled (if we don't care about direction), is #42+21=63# #m#.

The displacement (when we do care about direction) is #42-21=21# #m# #N#. Note that I included a direction.

The total time for both movements is #6+7=13# #s#.

The average speed is #"distance"/"time"=63/13=4.9# #ms^-1#

The average velocity is #"displacement"/"time"=21/13=1.6# #ms^-1# North.