Question

A car moves from A to B with a uniform speed u and returns to B with a uniform speed v. What is the average speed for this round trip?

Answer 1

Let distance travelled in going from A to B = x

Hence distance travelled back from B to A = x

Total Distance = 2x

Time for forward trip = x/vu

Time for return trip = x/vd

Hence total time = x/vu + x/vd

Average speed = Total distance/Total time = 2x / (x/vu + x/vd) = 2(vu)(vd) / (vu+vd)