【单选题】关于力的投影,下列说法正确的是?
C.
力在轴上投影的正负号主要是看力矢量箭头指向。
【简答题】矩形截面杆两端受载荷P作用,如图5-21所示。设杆件的横截面积为A,则下列结论中()是正确的。 1在截面m-m上的法向内力N=Pcosα。 2在截面m-m上的切向内力(剪力)Q=Psinα。 3在截面m-m上的正应力σ=P/A
sinα。 4在截面m-m上的剪应力τ=P/A
cosα。A. .①② B. ③④ C. 全对 D. 全错
【简答题】在图示平面桁架中,所有杆件的E皆相同,CA,AB,BF三杆的横截面面积为30cm 2 ,其余各杆的截面面积均为15cm 2 。a=6m,F=130kN。试求AB杆的轴力。
【判断题】在操作电动车窗时,如果出现某个机械部位卡死,则会引起熔丝烧断或热敏开关断开,从而避免电机被烧坏。
【单选题】听力原文:M: Anne, are you sure you'd like to have a house in Lark Green? Don't you think it a bit too far from town? W: I'd love to live there, Jack. I think the building site there is perfect. Open count...
A.
It's a delightful little town.
B.
It has a marvelous view.
C.
It is not far from the town.
D.
The house is built in open country.
【单选题】Green building does not specifically emphasize the issue of the________ existing homes.
【单选题】Green tourism does not create green jobs, including sustainability operations, energy efficiency and renewable technologies, environmental management, natural resource conservation, smart growth, buil...
【判断题】在操作电动车窗时,如果出现某个机械部位卡死,则会引起熔断丝烧断或热敏开关断开,从而避免电动机被烧坏。
【判断题】在迈克尔逊干涉仪中,当观察到圆环形干涉条纹时,这是属于等厚干涉。( )
【简答题】在迈克尔逊干涉仪中,当观察到圆环形干涉条纹时,这是属于 干涉