The car traveled all the way at an average speed of 54 km / h. Determine the speed on the first and second half

| January 19, 2021 | education

The car traveled all the way at an average speed of 54 km / h. Determine the speed on the first and second half of the journey, if it is known that the first half of the journey was driven by the car at a speed one and a half times greater than the second.

Vav = 54 km / h = 15 m / s.
V1 = 3 * V2 / 2.
S1 = S2 = S / 2.
V1 -?
V2 -?
The average speed of movement Vav is determined by the formula: Vav = S / t, where S is the entire path traveled by the body, t is the time of the entire movement.
t = t1 + t2.
t1 = S1 / V1 = S / 2 * V1 = S * 2/2 * 3 * V2 = S / 3 * V2.
t2 = S2 / V2 = S / 2 * V2.
t = t1 + t2 = S / 3 * V2 + S / 2 * V2 = 5 * S / 6 * V2.
Vav = S * 6 * V2 / 5 * S = 6 * V2 / 5.
V2 = 5 * Vav / 6.
V2 = 5 * 15 m / s / 6 = 12.5 m / s.
V1 = 3 * 12.5 m / s / 2 = 18.75 m / s.
Answer: the speed in the first half was V1 = 18.75 m / s, the speed in the second half was V2 = 12.5 m / s.



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