# An object travels North at 9 m/s for 2 s and then travels South at 7 m/s for  3 s. What are the object's average speed and velocity?

Apr 4, 2018

The average speed is $= 7.8 m {s}^{-} 1$. The average velocity is $= 0.6 m {s}^{-} 1$

#### Explanation:

The total distance travelled is

$d = \left(9 \cdot 2\right) + \left(7 \cdot 3\right) = 18 + 21 = 39 m$

The total time is $t = 2 + 3 = 5 s$

The average speed is

$\overline{v} = \frac{d}{t} = \frac{39}{5} = 7.8 m {s}^{-} 1$

The effective distance travelled is ${d}_{1} = 18 - 21 = - 3 m$

The average velocity is ${v}_{1} = | {d}_{1} \frac{|}{t} = \frac{3}{5} = 0.6 m {s}^{-} 1$