Question

An object travels North at `3 m/s` for `8 s` and then travels South at `4 m/s` for `2 s`. What are the object's average speed and velocity?

Answer 1

We must recall the definitions of average speed and average velocity.

Average speed: the change in distance divided by the total time

Average velocity: the DISPLACEMENT divided by the total time

remember that DISPLACEMENT is the distance from the initial point and the final point. So if I ran one lap around the track field, my displacement would actually be .... 0 meters.

So, we want to find the total distance that we traveled, both North and South.

traveling 3 m/s for 8 s would mean that we traveled for 24 meters total, North.

traveling 4 m/s for 2 s would mean that we traveled for 8 meters total, South.

Therefore, our total distance is 32 meters. The time it took was 10 seconds (8s north and 2s south), so the average speed is
`32/10 = 3.2m/s`

Part 2
Our total DISPLACEMENT is going to be 24 north + 8 south, or basically if we take north as the positive direction, # 24+(-8)# or 16 meters positive, or 16 meters north.

Our total time is still 10 seconds, so our average velocity is

`16/10 = 1.6` m/s North