# An object travels North at # 8 m/s# for #6 s# and then travels South at # 7 m/s# for # 4 s#. What are the object's average speed and velocity?

##### 2 Answers

Average speed

Average velocity

#### Explanation:

#### Explanation:

The distance North,

#s_n = v_n*t_n = 8 m/s*6 s = 48 m#

The distance Sorth,

#s_s = v_s*t_s = 7 m/s*4 s = 28 m#

**Average speed**

#"Average speed " = "total distance"/"total time" " "# So, plugging in our data,

#"Average speed " = (48 m + 28 m)/(6 s + 4 s) = (76 m)/(10 s)#

#"Average speed" = 7.6 m/s#

**Average velocity**

#"Average velocity " = "total displacement"/"total time"#

To determine displacement, we need a rule for what the positive direction is. I declare that North is the positive direction. So, plugging in our data,

#"Average velocity" = (48 m - 28 m)/(6 s + 4 s) = (20 m)/(10 s)#

#"Average velocity" = 2.0 m/s#

I hope this helps,

Steve