Answer to Question #4057 in Mechanics | Relativity for Dai
Question #4057
Sally travels by car from one city to another. She drives for 27.0 min at 72.0 km/h, 54.0 min at 33.0 km/h, and 39.0 min at 74.0 km/h, and she spends 8.0 min eating lunch and buying gas.
(a) Determine the average speed for the trip.
(a) Determine the average speed for the trip.
Expert's answer
First, let's admit that
27.0 min = 27/60 h = 9/20 h;
54.0 min = 54/60 h = 9/10 h;
39.0 min = 39/60 h = 13/20 h.
Then, time spent on a trip is
T = 9/20 + 9/10 + 13/20 = 2h.
Total distance is
D = 9/20*72 + 9/10*33 + 13/20*74 = 551/5 km.
So, average speed for the trip is
V = D/T = 551/5/2 = 55.1 km/h.
27.0 min = 27/60 h = 9/20 h;
54.0 min = 54/60 h = 9/10 h;
39.0 min = 39/60 h = 13/20 h.
Then, time spent on a trip is
T = 9/20 + 9/10 + 13/20 = 2h.
Total distance is
D = 9/20*72 + 9/10*33 + 13/20*74 = 551/5 km.
So, average speed for the trip is
V = D/T = 551/5/2 = 55.1 km/h.
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Comments
ans 51.65 Km/hr
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