# An object travels North at 4 m/s for 9 s and then travels South at 8 m/s for  2 s. What are the object's average speed and velocity?

Jun 26, 2016

Avg. Speed = 4.7 m/s
Avg. Velocity = 1.8 m/s

#### Explanation:

Total distance traveled = 4 * 9 + 8 * 2 = 52 m
Total time = 9+2 = 11 s.
Average speed = 52/11 = 4.7 m/s

Total displacement = 4 * 9- 8 * 2 = 20 m

(Note The second travel is subtracted because it is at 180 degrees with the first travel. The projection of that vector on the first can be found by multiplying it with Cos180 = -1)

Average velocity = 20/11 = 1.8 m/s