The boy walked for some time at a speed of 4 km / h, carrying the bike in his hands, and then the same amount

| September 3, 2021 | education

The boy walked for some time at a speed of 4 km / h, carrying the bike in his hands, and then the same amount of time cycled at a speed of 16 km / h. Calculate the average speed of the boy along the entire path.

V1 = 4 km / h.

V2 = 16 km / h.

t1 = t2 = t / 2.

Vav -?

To find the average speed of the boy’s movement Vav, it is necessary to divide the entire path S during which he moved by the time of his movement t: Vav = S / t.

The entire path of the boy S can be represented as a sum: S = S1 + S2, where S1 is the path traveled on foot, S2 is the path that the boy traveled on his bicycle.

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

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

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

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

Vav = (4 km / h + 16 km / h) / 2 = 10 km / h.

Answer: the boy’s average speed was Vav = 10 km / h.



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