V1 = 20 m / s.
V2 = 30 m / s.
To find the average speed of movement Vav, it is necessary to divide the entire path S passed by the body by the time of its passage t: Vav = S / t.
The travel time of the entire path is expressed by the sum: t = t1 + t2, where t1 is the time of movement on the first part of the path, t2 is the time of movement on the second part of the path.
The path S traversed by the body will be the sum: S = S1 + S2.
With uniform movement, the distance traveled on the first part of the path S1 is expressed by the formula: S1 = V1 * t1.
S2 = V2 * t2.
S = V1 * t1 + V2 * t2.
The average body speed Vav will be determined by the formula: Vav = (V1 * t1 + V2 * t2) / (t1 + t2).
Vav = (20 m / s * t1 + 30 m / s * t2) / (t1 + t2).
Answer: the average body speed is Vav = (20 m / s * t1 + 30 m / s * t2) / (t1 + t2).
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