The cyclist, moving downhill, covered the distance between two points at a speed of 15 km / h.
| February 13, 2021 | education
The cyclist, moving downhill, covered the distance between two points at a speed of 15 km / h. On the way back, he was going twice as slow. What is the average speed along the way?
Let the distance between points be s.
Time spent on descent between points with a speed v1 = 15 km / h:
t1 = s / v1.
The cyclist rode upward at a speed v2 = v1 / 2.
Time was spent on the ascent:
t2 = s / v2 = s / (v1 / 2) = 2s / v1.
Travel time:
t = t1 + t2 = s / v1 + 2s / v1 = 3s / v1.
Average speed is equal to the sum of the distances over the total travel time:
vc = 2s / t = 2s / (3s / v1) = 2v1 / 3 = (2 * 15 km / h) / 3 = 10 km / h.
Answer: the average speed is 10 km / h.
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