Answer to Question #22008 in Mechanics | Relativity for ololade
V·(T1 + T2) = V1·T1 + V2·T2 (1)
A cyclist spent
T1 = 20[km]/20[km/h] = 1[h]
riding the first 20km at 20km/h. Also, he spent
T1 = S2/V2
riding the second 20km. So, we can rewrite (1) as
V·(T1 + S2/V2) = V1·T1 + V2·S2/V2,
V·T1 + V·S2/V2 = V1·T1 + S2 ==>
V2 = V·S2 / ( V1·T1 + S2 - V·T1 ) =
= 10[km/h]·20[km] / (20[km/h]·1[h] + 20[km] - 10[km/h]·1[h] ) =
= 10[km/h]·20[km] / 30[km] = 20/3 [km/h].
Therefore, the speed required for the final 20km if the average speed for the trip to be 10km/h is 20/3 [km/h].
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