Вопрос школьника по предмету Физика
середня швидкість руху автомобіля на всьому шляху дорівнює 100км/год.Першу третину автомобіль рухався із середньою швидкістю 120км/год. Визначити середню швидкість на останній частині шляху.(90км/год)
Ответ учителя по предмету Физика
Пусть S — длина пути.
V=100 км/ч
Время первой трети пути:
t1 = S/(3*120)
Время на остальной части пути:
t2=2S/(3x)
Общее время:
t = t1+t2 = S*(1/360+2/(3x))
Средняя скорость на всем участке:
V=S/t = S / (t1+t2) = 1 /(1/360+2/(3*x))
По условию
V=100
100=1/ (1/360+2/(3x))
Отсюда:
x= 90 км/ч
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