Determine the average speed of a soldier crawling, if 1/5 of the way to the tank he crawled at a speed of 0.15 m / s, the next third of the remaining path he covered twice as fast, and the remaining path he covered at a speed of 0.1 m / s from.
Average travel speed:
Vav. = S / t, where S is the total distance traveled, t is the total time of movement.
S = S1 + S2 + S3, where S1 = 1 / 5S, S2 = 4/5 S * (1/3) = 4/15 S, S3 = 4 / 5S * (2/3) = 8/15S.
t = t1 + t2 + t3.
S1 = V1 * t1, S2 = V2 * t2, S3 = V3 * t3, where V1 = 0.15 m / s, V3 = 0.1 m / s.
Travel time when passing S1, S2, S3:
t1 = S1 / V1 = (1 / 5S) / 0.15; t2 = t1 / 2 = ((1 / 5S) / 0.15) / 2; t3 = S3 / V3 = (8 / 15S) / 0.1.
Vav. = S / ((1 / 5S) / 0.15 + ((1 / 5S) / 0.15) / 2 + (8 / 15S) / 0.1) = 1 / (1.33 + 0.67 + 5.33) = 1 / 7.3 = 0.136 m / s.
Answer: The average speed of a fighter is 0.136 m / s.
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