ch02-p013 - 13. (a) Denoting the travel time and distance...

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avg1 (55 km/h)( /2) (90 km/h)( / 2) 72.5 km/h DT T s TT + == = which should be rounded to 73 km/h. (b) Using the fact that time = distance/speed while the speed is constant, we find avg2 /2 55 km/h 90 km/h 68.3 km/h DD s T = + which should be rounded to 68 km/h. (c) The total distance traveled (2 D ) must not be confused with the net displacement (zero). We obtain for the two-way trip avg 72.5 km/h 68.3 km/h 2 70 km/h. D s + (d) Since the net displacement vanishes, the average velocity for the trip in its entirety is zero. (e) In asking for a sketch , the problem is allowing the student to arbitrarily set the distance D (the intent is not to make the student go to an Atlas to look it up); the student can just as easily arbitrarily set
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