如图表示的是一个在细绳的结点O上悬挂重物的装置，细绳AO和BO的A、B端都是固定的．平衡时AO是水平的，BO与竖直方向的夹角为θ．若已知重物的重力为mg，求：
（1）AO的拉力F1的大小；
（2）BO的拉力F2的大小．
（1）对点O受力分析，受重力、两根绳子的拉力，如图
将两根绳子的拉力合成，合力与重力平衡，故
F12合=T=mg
F1=mgtanθ
（2）F2=mg cosθ
另
F2y=T=mg
F1=F2x=F2ytanθ=mgtanθ
F2=
=F2y cosθ mg cosθ
答：（1）AO的拉力F1的大小为mgtanθ；
（2）BO的拉力F2的大小为
．mg cosθ
English is a language spoken all round the world.There are more than 42 _56___ where most of people speak English. Most native speakers of English are found in the United Kingdom,the United States of American ,Canada, Australia, South Afiran, Ireland and New Zealand. In total,for more than 375 million people. English is their __57__language.These people will perhaps speak the language of their own country_58____with their family, but the language of the government ,shool, newspapers and TV is English. We find this situation in countries,_59__ India,Pakistan,Nigeria and the Philippines. Howerer ,a lot of of people learn English as a foreign __60__.They are more than 750 million, Everywhere in the world children go to school __61___English.Most people learn English for five or six years at high schools. In China students learn English at school _62__a foreign language. In only fifty years English has developed into the language _63____spoken and used in the world. English is the _64__language of the most international organizations(组织),international trade( 贸易 ) and tourism. Business and tourists often come to China_65__being able to speak Chinese. English is also the language of global(全球的) culture,such as popular music and Internet.
|