The car drove the first half of the journey at a speed of 60 km / h. At what speed did the car travel the second half of the way, if the average speed of its movement along the entire route is 48 km / h?
Initial data: V1 (vehicle speed in the first half of the journey) = 60 km / h; Vav. (average car speed) = 48 km / h; S1 = S2 = 0.5S.
The speed of the body on the second section of the path is found from the formula for calculating the average speed:
Vav. = S / (t1 + t2) = S / (0.5S / V1 + 0.5S / V2) = 1 / (1 / 2V1 + 1 / 2V2).
48 = 1 / (1 / (2 * 60) + 1 / 2V2).
1/48 = 1/120 + 1 / 2V2.
1 / 2V2 = 1/48 – 1/120 = 5/240 – 2/240 = 3/240.
2V2 = 240/3 = 80.
V2 = 40 km / h.
Answer: The car passed the second section of the route at a speed of 40 km / h.
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