问题 计算题

如图所示,质量分别为m1、m2的两个物块,中间用细绳相连,在F拉力的作用下一起向上做匀加速运动,求中间细绳的拉力为多大?

答案

两个物块具有共同的加速度,把他们看作整体,根据牛顿第二定律可得:

解得:加速度

再隔离后面的物块m1,它受重力G、和拉力T两个力作用,根据牛顿第二定律可得:

带入可得: 

由以上两个例题可得:对于在已知外力求内力的连接体问题中,系统中各物体的内力是按照质量关系分配牵引力的。只与连接体系统的质量和牵引力有关,与系统的加速度a、摩擦因数μ、斜面倾角θ无关。

选择题
阅读理解

任务型阅读。

认真阅读下列短文,并根据所读内容在文章后表格中的空格里填入一个最恰当的单词.

注意:每个空格只填1 个单词.请将答案写在答题卡相应题号的横线上.

     In the far north-eastern corner of South Africa, Kruger National Park is the largest

game reserve (野生动植物保护区) in the country, and the most famous wildlife zone

on the African continent. Stretching out over 7,332 square miles, Kruger is a wonderland

of wildlife. It has 507 species of birds and 147 species of mammals. It also has a fair bit

of history  it dates back to 1898 when it was founded as a game reserve in an attempt to

control hunting in the area. It didn't see a tourist until 1927; however, one year later it

became a national park.

     It's a good place to see roaring beasts in their own backyards. South Mrica is an

increasingly hot tourist spot, and you may want to visit it this year, before it hosts the

2010 football World Cup. South Africa is also an inexpensive country for tourists.

     Anyone seeking to escape the European winter will be surprised to hear that March

is not the best time to go to Kruger.

     The six-month period between May and October tends to be the most suitable time

for wildlife - spotting. The weather is not only cooler but also considerably drier. This

means that water sources dry up and animals are forced to approach rivers, creeks, dams

and watering holes in search of liquid refreshment.

      If you go to South Africa, you need to pay attention to the threat of malaria (疟疾).

Kruger is one of the only two South African national parks that have an issue about the

disease, but only during the rainy season ( December to April).

       A disadvantage of Kruger is that it sits a long way from South Africa's other well-known

tourist attractions  Cape Town, the Garden Route, and the meeting of the Atlantic and Indian

Oceans at Cape Agulhas.