如图所示，光滑斜面上有两个不同质量的物体a、b，用轻杆将两者连_爱下问搜题

搜题请搜索小程序“爱下问搜题”

问题选择题

如图所示，光滑斜面上有两个不同质量的物体a、b，用轻杆将两者连接．静止释放a、b后，以下说法中正确的是（　　）

A．杆对a的作用力沿斜面向上

B．杆对b的作用力沿斜面向上

C．杆对两物体的作用力都为零

D．无法判断杆产生的作用力方向

答案

设斜面的倾角为α，杆对a的作用力大小为F，方向沿斜面向下．

根据牛顿第二定律得：

对整体：（m_a+m_b）gsinα=（m_a+m_b）a

对a：：m_agsinα+F=m_aa

联立上两式解得，F=0，说明杆对a没有作用力，则杆对b也没有作用力．故C正确，A、B、D错误．

故选C

填空题

词汇运用。用括号内所给词的适当形式填空。（每空不限一词）

1. Who is ______ (healthy), Tom, Jack, or David?

2. The children are looking forward to ______ (ski) with their parents.

3. The clothes and shoes are the ______ (run).

4. Daniel likes sports, Nick is a little ______ (sport) than him.

5. I remember ______ (see) you somewhere in Nanjing.

6. Do you know the ______ (long) of the river.

7. Cows' ______ (stomach) are far bigger than sheep's.

8. They were very tired because of the ______ (please) trip.

9. What makes you ______ (think) he is a fool.

10. Simon and Linda looked at each other. They kept their secret to ______ (they).

单项选择题

关于维生素D的生理功能，哪项是不正确（）

A.促进小肠黏膜对钙磷的吸收

B.促进肾近曲小管对钙磷的重吸收

C.促进破骨细胞的形成

D.抑制旧骨的吸收

E.促进骨盐沉积于成骨细胞周围，利于新骨形成