Объяснение:
Дано:
Q = 45 кН
α = 25°
β = 60°
___________
F₁ - ?
F₂ - ?
1)
Считаем стержни сжатыми.
2)
Освобождаемся от связей, делаем чертеж.
3)
sin 25° = 0,4226
cos 25° = 0,9063
sin 60° = 0,8660
cos 60° = 0,5000
Находим проекции сил на оси.
Ось ОХ:
Q + F₁·cos 25° - F₂·cos 60 = 0
или
0,9063·F₁ - 0,5000·F₂ = -45 (1)
Ось ОY:
F₁·sin 25° + F₂·sin 60° = 0
или
0,4226·F₁ + 0,8660·F₂ = 0 (2)
Из (2):
F₂ = - (0,4226/0,8660)·F₁ = - 0,488·F₁
Тогда (1):
0,9063·F₁ + 0,5000·0,488·F₁ = -45
F₁ = - 39 кН (стержень растянут)
F₂ = -0,488·(-39) ≈ 19 кН
In the 19th century, football in England gained a popularity comparable to cricket [15]. It was played mainly in colleges [16]. In some colleges, the rules allowed dribbling and passing the ball by hand, in others it, on the contrary, was prohibited. [17] The first attempt to create uniform rules was made in 1846, when representatives of several colleges met. They established the first set of rules [18]. The first specialized football club was founded in 1857
Sheffield [19]. In 1863, after lengthy negotiations, a set of rules for the Football Association of England was adopted. The sizes of the field and the goal were also adopted [20]. And in 1871, the FA Cup was founded - the oldest football tournament in the world [21]. In 1891, the penalty rule was adopted. But at first, the penalty was fired not from the point, but from the line, which, like now, was at a distance of 11 meters from the goal [22]. According to the Rules, the mandatory elements of equipment are: a shirt (or T-shirt) with sleeves, shorts, leggings, shin guards and boots
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