A person travels from A to B, distance D, with speed u, remains at B for time τ and returns to A with speed v. The average speed for the complete trip is:
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Question

A person travels from A to B, distance D, with speed u, remains at B for time τ and returns to A with speed v. The average speed for the complete trip is:

G1 Physics · Accepted Answer

Total distance = 2D. Total time = D/u + τ + D/v = [D(u+v) + uvτ]/(uv). Therefore Average speed = 2D / total time = 2Duv/[D(u+v)+uvτ].