V_{сер} = (l1 + l2)/(t1+t2), l1=l2, t1 = l1/v, t2 = l2/3v
V_{сер} = 6v/4=3v/2
ответ : U ср = 3v/2
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V_{сер} = (l1 + l2)/(t1+t2), l1=l2, t1 = l1/v, t2 = l2/3v
V_{сер} = 6v/4=3v/2
ответ : U ср = 3v/2
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