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.

An object travels North at 7 7 ms^-1ms^-1 for 66 ss and then travels South at 3 3 ms^-1 ms^-1 for 7 7 s s. What are the object's average speed and velocity?