# An object travels North at  3 m/s for 7 s and then travels South at  4 m/s for  4 s. What are the object's average speed and velocity?

Apr 23, 2018

#### Explanation:

The total distance travelled is

$d = \left(3 \times 7\right) + \left(4 \times 4\right) = 37 m$

The time to cover this distance is

$t = 7 + 4 = 11 s$

The average speed is

$\overline{v} = \frac{d}{t} = \frac{37}{11} = 3.36 m {s}^{-} 1$

The effective distance travelled is

${d}_{1} = \left(3 \times 7\right) - \left(4 \times 4\right) = 5 m$

The average velocity is

${v}_{a} = {d}_{1} / t = \frac{5}{11} = 0.45 m {s}^{-} 1$