The motorcyclist drove 0.4 of the way between the two cities at a speed of 20 m / s

The motorcyclist drove 0.4 of the way between the two cities at a speed of 20 m / s, and the rest of the way at a speed of 54 km / h. Determine the average speed of the motorcyclist.

Problem data: S1 (distance between two cities) = 0.4S; V1 (speed of a motorcyclist between two cities) = 20 m / s; S2 (length of the remaining part of the path) = 0.6S; V2 (motorcycle speed on the rest of the way) = 54 km / h (in SI V2 = 15 m / s).

The average speed of this motorcycle is calculated by the formula: Vav. = S / (t1 + t2) = S / (S1 / V1 + S2 / V2) = S / (0.4S / V1 + 0.6S / V2) = 1 / (0.4 / V1 + 0.6 / V2).

Let’s make a calculation: Vav. = 1 / (0.4 / 20 + 0.6 / 15) = 1 / 0.06 = 16.67 m / s (60 km / h).