Unformatted text preview: decimal form, the time left is 1.25 hour, and the distance that remains is 160 km. Thus, a speed v = (160 km)/(1.25 h) = 128 km/h is needed. The WileyPlus numbers require a little more computation, but use t = d/v to get the time for each of the first two segments. Then work out the remaining distance and remaining time to find the speed needed. 2P13. (a) Denoting the travel time and distance from San Antonio to Houston as T and D, respectively, the average speed is D (55 km/h)(T/2) + (90 km/h)(T / 2)
savg1 = =
= 72.5 km/h T
T which should be rounded to 73 km/h. (b) Using the fact that time = distance/speed while the speed is constant, we find D
D
savg2 = = D / 2
= 68.3 km/h /2
T 55 km/h + 90Dkm/h which should be rounded to 68 km/h....
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 Spring '14
 Physics, Work, Orders of magnitude, m/s

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