<PRE><B>Question 715228</B>
The average velocity is equal to the average of the initial and final velocities ONLY if the acceleration is constant.
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Suppose you travel up a hill at 40 miles/hour and then return down the hill at 60 miles/hour.
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Distance up = Distance down = x miles
time up = x/40 mph 
time down = x/60 mph
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Average speed is given by the total distance traveled divided by the total time.  
a) What was your average speed for the round trip journey?
= total distance/total time = 2x/(x/40 + x/60) = 2x/(100x/2400) = 2*24 = 48 mph
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In general, average velocity is given by the change in displacement divided by the time interval.
b) What was your average velocity?
= 0/(x/40 - x/60) = 0/(20x/2400) = 0 
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Cheers,
Stan H.
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