题干

如图,一小车上有一个固定的水平横杆,左边有一轻杆与竖直方向成θ角与横杆固定,下端连接一质量为m的小球P.横杆右边用一根细线吊一相同的小球Q.当小车沿水平面做加速运动时,细线保持与竖直方向的夹角为α.已知θ<α,则下列说法正确的是(   )

A:小车一定向右做匀加速运动

B:轻杆对小球P的弹力沿轻杆方向

C:小球P受到的合力大小为mgtanθ

D:小球Q受到的合力大小为mgtanα

上一题 下一题 0.0难度 选择题 更新时间:2019-07-25 07:10:21

答案(点此获取答案解析)

A,D

同类题3

   About 21,000 young people in 17 American states do not attend classes in school buildings.
   Instead, they receive their elementary and high school education by working at home on computers. The center for Education Reform says the United States has 67 public “cyberschools(网络学校)” and that is about twice as many as two years ago.
   The money for students to go to a cyberschool comes from the governments of the states where they live. Some educators say cyberschools receive money that should support traditional public schools. They also say it is difficult to know if students are learning well.
Other educators praise this new form of education for letting students work at their own speed. These people say cyberschools help students who were unhappy or unsuccessful in traditional schools. They say learning at home by computer ends long bus rides for children who live far from school.
   Whatever the judgment of cyberschools, they are getting more and more popular. For example, a new cyberschools called Commonwealth Connections Academy will take in students this fall. It will serve children in the state of Pennsylvania from ages five through thirteen.
Children get free equipment for their online education. This includes a computer, a printer, books and technical services. Parents and students talk with teachers by telephone or by sending emails through their computers when necessary.
   Students at cyberschools usually do not know one another. But 56 such students finished studies at Western Pennsylvania Cyber Charter School recently met for the first time. They were guests of honor at their graduation.