# An object travels North at 8 m/s for 7 s and then travels South at 3 m/s for 9 s. What are the object's average speed and velocity?

Dec 15, 2017

The average speed is $= 5.1875 m {s}^{-} 1$. The average velocity is$= 1.8125 m {s}^{-} 1$

#### Explanation:

Total distance travelled is $d = \left(8 \times 7\right) + \left(3 \times 9\right) = 56 + 27 = 83$

Total time is $t = 7 + 9 = 16 s$

The average speed is

$\overline{v} = \frac{d}{t} = \frac{83}{16} = 5.1875 m {s}^{-} 1$

The distance from the starting point is

${d}_{1} = \left(8 \times 7\right) - \left(3 \times 9\right) = 56 - 27 = 29 m$

The time is the same

The average velocity is

$= \frac{29}{16} = 1.8125 m {s}^{-} 1$