An object travels North at $9 m/s$ for $4 s$ and then travels South at $3 m/s$ for $1 s$ . What are the object's average speed and velocity?

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Answer 1 · 2018-05-09T15:36:11

$"average speed" = 7.8 m/s$ and $"average velocity" = 6.6 m/s$

While going North, the object goes $9 m/cancel(s) * 4 cancel(s) =36 m$ .

While going South, the object goes $3 m/cancel(s) * 1 cancel(s) =3 m$ .

For average speed , direction does not matter, just total distance and total time.

$"average speed" = "total distance"/"total time" = (36 m+3 m)/(4 s + 1 s) = 7.8 m/s$

For average velocity, direction does matter, so we need the resultant of all displacements (which are vectors) and total time.

$"average velocity" = "net displacement"/"total time" = (36 m-3 m)/(4 s + 1 s) = 6.6 m/s$ to the North.

I hope this helps,
Steve

An object travels North at 9 m/s9 m/s for 4 s4 s and then travels South at 3 m/s3 m/s for 1 s 1 s. What are the object's average speed and velocity?