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mechanics 2

發問:

You drive the 4600 km from coast to coast of the United States at 65 mi/h (105 km/h), stopping an average of 30 min for rest and refueling after every 2 h of driving. a) What is your average velocity for the entire trip? b) How long does the trip take? ans: a) 84 km/h b) 55 h Thanks~~

最佳解答:

(a) Let t be the time duration that you are driving the car Hence, 4600 = 105t t = 4600/105 hours = 43.81 hours No. of resting = 43.81/2 = 22 Total resting time = 22 x 0.5 hours = 11 hours Therefore, total time of the journey = (43.81 + 11) hours = 54.81 hours Average velocity = 4600/54.81 km/h = 84 km/h (b) The total journey time, as calculated in (a), is 55 hours round up to the nearest hour).

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