# An object travels North at 6 m/s for 9 s and then travels South at 6 m/s for 7 s. What are the object's average speed and velocity?

Feb 20, 2017

The average speed is 6m/s; the average velocity is 0.75 m/s North.

#### Explanation:

First, we must determine the displacement of the object during each time interval.

During the first 9s

$d = v \times t = 6 \frac{m}{s} \times 9 s = 54 m$ North

During the next 7s

$d = v \times t = 6 \frac{m}{s} \times 7 s = 42 m$ South

For the average speed , we consider only the total distance travelled and the total time taken

${v}_{\text{ave}} = d \div t = 96 m \div 16 s = 6 \frac{m}{s}$

For the average velocity , we consider the net displacement and the time taken. The net displacement has been only 12 m North.

${\vec{v}}_{\text{ave}} = \vec{d} \div t = 12 m N \div 16 s = 0.75 \frac{m}{s}$ North