An object travels North at # 3# #ms^-1# for #6# #s# and then travels South at # 4 # #ms^-1# for # 4 # #s#. What are the object's average speed and velocity?

1 Answer
David G.
May 13, 2017

speed = 3.4# #ms^-1#

velocity = 0.2# #ms^-1# North

Explanation:

The average speed is the total distance traveled divided by the total time.

In this case, the object travels #3xx6=18# #m# North and then #4xx4=16# #m# South. That means it travels a total of #18+16=34# #m# in #6+4=10# #s#, so

speed = distance/time = #34/10 = 3.4# #ms^-1#

The average velocity is the final displacement from the start point, divided by the total time. Since the object traveled #18# #m# North and then changed direction and traveled #16# #m# South, the displacement is #2# #m# North (remember, displacement and velocity are vector quantities, so we must specify direction).

velocity = displacement/time = #2/10 = 0.2# #ms^-1# North

(also, it really helps to draw a diagram)

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