The skier covered the first half of the journey at a speed 3 times faster than the second. Vaverage-7.5 kmph. Find V2.
| September 17, 2021 | education
V1 = 3 * V2.
S1 = S2 = S / 2.
Vav = 7.5 km / h.
V2 -?
The average speed of movement Vav is determined by the formula: Vav = S / t, where S is the entire path traveled by the skier, t is the time of movement along the entire path.
The time of movement along the entire path t is found by the formula: t = t1 + t2, where t1 is the time of movement on the first half of the path, t2 is the time of movement on the second half of the path.
t1 = S1 / V1 = S / 2 * V1 = S / 2 * 3 * V2.
t2 = S2 / V2 = S / 2 * V2.
t = S / 6 * V2 + S / 2 * V2 = (S + 3 * S) / 6 * V2 = 2 * S / 3 * V2.
Vav = S * 3 * V2 / 2 * S = 3 * V2 / 2.
V2 = 2 * Vav / 3.
V2 = 2 * 7.5 km / h / 3 = 5 km / h.
Answer: the speed of the skier in the second half is V2 = 5 km / h.
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