Мячик массой 300 г бросили со скоростью 6м/с вертикально вверх. за какое время мячик поднимется на максимальную высоту? сопротивлением воздуха пренебречь. 1) 0, 6 с 2) 1, 8 3)2 4)6

V= v0- gt v=0 v0=gt t= v0/ g t= 6 /10=0,6 c

за  20 сек  первый успеет проехать:

so  = (1/2) • at2  = (1/2) • 0.4 × 202  = 80 м, при этом его скорость будет:   vo  = at = 0.4 × 20 = 8 м/c.

далее составим уравнения движения для первого и для второго, посчитав за начало отсчёта момент, когда стартовал второй.

x1  = so  + vot + (1/2) • at2.

x2  = (1/2) • at2.

разница  x1  − x2  есть расстояние между велосипедистами и в какой-то момент оно равно  l = 240 м.

so  + vot = l.

t = (l − so)/vo  = (240 − 80)/8 = 20 c.

ответ:   20 с.

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