# An object travels North at 2 m/s for 9 s and then travels South at 4 m/s for 1 s. What are the object's average speed and velocity?

Feb 1, 2018

The average speed is $= 2.2 m {s}^{-} 1$.
The average velocity is $= 1.4 m {s}^{-} 1$

#### Explanation:

The total distance travelled

$s = \left(2 \cdot 9\right) + \left(4 \cdot 1\right) = 18 + 4 = 22 m$

The total time is

$t = {t}_{1} + {t}_{2} = 9 + 1 = 10 s$

The average speed is

$\overline{u} = \frac{s}{t} = \frac{22}{10} = 2.2 m {s}^{-} 1$

The real distance travelled is

$d = \left(2 \cdot 9\right) - \left(4 \cdot 1\right) = 18 - 4 = 14 m$

The total time is

$t = {t}_{1} + {t}_{2} = 9 + 1 = 10 s$

The average velocity is

$\overline{v} = \frac{d}{t} = \frac{14}{10} = 1.4 m {s}^{-} 1$