An object travels North at #8# #ms^-1# for #9# #s# and then travels South at #5# #ms^-1# for #3# #s#. What are the object's average speed and velocity?

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Answer 1 · 2017-07-10T07:06:16

Average speed = #("total distance traveled")/("total time taken")=93/12=7.75# #ms^-1#

Average velocity = #("total displacement")/("total time taken")=63/12=5.25# #ms^-1# #N#

Distance traveled North:

#s_N=ut=8xx9=72# #m#

Distance traveled South:

#s_S = ut = 5xx3=15# #m#

Total distance traveled:

#s=s_N+s_S=78+15=93# #m#

Total time:

#t=9+3=12# #s#

Average speed = #("total distance traveled")/("total time taken")=93/12=7.75# #ms^-1#

If we take North as the positive direction, total displacement:

#s=s_N-s_S=78-15=63# #m# #N#

This is the distance of the object from its starting point, and includes a direction.

Average velocity = #("total displacement")/("total time taken")=63/12=5.25# #ms^-1# #N#