An object travels North at 4 m/s for 3 s and then travels South at 1 m/s for  6 s. What are the object's average speed and velocity?

Jan 2, 2018

The average speed is $= 2 m {s}^{-} 1$. The average velocity is

$= \frac{2}{3} m {s}^{-} 1$

Explanation:

The total distance travelled is

$d = \left(4 \cdot 3 + 1 \cdot 6\right) = 12 + 6 = 18 m$

The time taken for the whole journey is

$t = 3 + 6 = 9 s$

The average speed is

$\overline{v} = \text{total distance travelled "/"total time taken} = \frac{18}{9} = 2 m {s}^{-} 1$

The effective distance travelled is

${d}_{e f f} = 4 \cdot 3 - 1 \cdot 6 = 12 - 6 = 6 m$

The time taken is

$t = 9 s$

The average velocity is

$= \text{effective distance travelled"/"time taken} = \frac{6}{9} = \frac{2}{3} m {s}^{-} 1$