The first half of the journey the car moved at a speed of 60 km / h, and the second half

| March 31, 2021 | education

The first half of the journey the car moved at a speed of 60 km / h, and the second half – at a speed of 100 km / h. Find the average vehicle speed.

V1 = 60 km / h.

V2 = 100 km / h.

S1 = S2 = S / 2.

Vav -?

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

The travel time of the entire path is found by the sum: t = t1 + t2, where t1, t2 are the travel times on the first and second half of the path.

t1 = S1 / V1 = S / 2 * V1.

t2 = S2 / V2 = S / 2 * V2.

t = S / 2 * V1 + S / 2 * V2 = (S * V2 + S * V1) / 2 * V1 * V2 = S * (V2 + V1) / 2 * V1 * V2.

Vav = S * 2 * V1 * V2 / S * (V2 + V1) = 2 * V1 * V2 / (V2 + V1).

Let us substitute the data from the condition of the problem: Vav = 2 * 60 km / h * 100 km / h / (100 km / h + 60 km / h) = 75 km / h.

Answer: the car was moving at an average speed Vav = 75 km / h.



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