The car drove the first 4 km at a speed of 20 km / h and the next 12 km at an average speed

| April 23, 2021 | education

The car drove the first 4 km at a speed of 20 km / h and the next 12 km at an average speed of 40 km / h. What is the average speed of the car along the entire route?

S1 = 4 km.

V1 = 20 km / h.

S2 = 12 km.

V2 = 40 km / h.

Vav -?

To find the average vehicle speed Vav, it is necessary to divide the entire path S it has traveled by the time of its passage t: Vav = S / t.

The entire path S and the time of the entire movement t of the car will be the sums: S = S1 + S2, t = t1 + t2.

Since the car moved uniformly in the first and second sections, we will express the driving time on each section, respectively: t1 = S1 / V1, t2 = S2 / V2.

t1 = 4 km / 20 km / h = 0.2 h.

t2 = 12 km / 40 km / h = 0.3 h.

t = 0.2 h + 0.3 h = 0.5 h.

S = 4 km + 12 km = 16 km.

Vav = 16 km / 0.5 h = 32 km / h.

Answer: the average speed of the car along the entire route is Vav = 32 km / h.



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