# An object travels North at  3 m/s for 9 s and then travels South at  5 m/s for  4 s. What are the object's average speed and velocity?

Jun 1, 2016

Average speed=$\frac{47}{13}$m/s

Average velocity=$\frac{7}{13}$m/s

#### Explanation:

In physics, the difference between speed and velocity is velocity account for direction, while speed doesn't. If an abject went one mile north and one mile south in one hour, it's average speed is 2mph wile its average velocity is 0. This is because speed is total distance covered divided by time, while velocity is displacement divided by time.

Speed Calculated: total distance= 3m/s(9s) + 5m/s(4s)= 47m traveled(unit of time cancels out). Total time 13s, so the average speed is $\frac{47}{13}$m/s.

Displacement is a bit more tricky. We have to assign a positive and negative direction. Let north be positive and south be negative. We do the same calculation for total distance traveled, except when the object travels in the negative direction we subtract it. This displacement= 3m/s(9s) - 5m/s(4s)= 7m. Divided by total time we get the average velocity, which is just displacement divided by total time, is $\frac{7}{13}$m/s.

Hope this helps.