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A car travels up a hill at a constant speed of 35 km/h and returns down the hill at a constant speed of 66 km/h. How to calculate the average speed for the round trip ?
in Physics
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Let D = total distance traveled;

Distance traveled in each journey is D/2

Time taken for going up the hill = t1;

Time taken for going down the hill = t2;

Total time taken = T = t1 + t2

Speed going uphill = v1 = 35 km/h

Speed going downhill = v2 = 66 km/h

Average speed is defined as the ratio of total distance traveled to total time taken = D/T

Thus, t1​ = (D/2)​ / v1 = (D/2) / 35 ​= D​/70

And t2​ = (D/2) / v2 ​= D/132

Therefore, average speed is vavg​ = D / (t1​ + t2​) ​= D / (D/70 + D/132) ​= 9240/202 = 45.74 km/h
by Diamond (39,278 points)

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