Зачем вам по столбиками. здесь просто нужно составить предложения: boys often run around in the classroom during the break. we often learn new words at the lesson girls sometimes draw funny pictures on the blackboard during the break boys usually talk loudly during the break we sometimes run and jump between the desks during the break we sometimes discuss different problems during the break teachers usually ask a lot of questions at the lesson teachers sometimes have a cup of tea or coffee during the break i sometimes read newspapers and wall newspapers during the break
F=mg
Объяснение:
масса доски m
L1=L*3/4
L2=L/4 - длина плеча для действующей силы
на длинную часть действует сила тяжести
mg*3/4 и приложенная сила к плечу L11=L*3/8
на короткую часть действует сила тяжести
mg/4 и приложенная сила к плечу L22=L/8
По правилу моментов.
(mg*3/4)*(L*3/8) = F*L/4 + (mg/4)*(L/8)
L*mg*9/32 = F*L/4 + (mg*L/32)
L*mg*9/8 = F*L + (mg*L/8)
L*mg*8/8 = F*L
mg = F
Нужно приложить силу равную весу доски.