An object travels North at 15 m/s for 3 s and then travels South at 12 m/s for 7 s. What are the object's average speed and velocity?

Jun 29, 2017

The average speed is $= 12.9 m {s}^{-} 1$
The average velocity is $= - 3.9 m {s}^{-} 1$

Explanation:

The total distance travelled is $d = 15 \cdot 3 + 12 \cdot 7 = 129 m$

The total time is $t = 3 + 7 = 10 s$

The average speed is

$\overline{v} = \frac{d}{t} = \frac{129}{10} = 12.9 m {s}^{-} 1$

The displacement is

$\Delta x = 15 \cdot 3 - 12 \cdot 7 = - 39 m$

The average velocity is

$= \frac{\Delta x}{t} = - \frac{39}{10} = - 3.9 m {s}^{-} 1$