工程力学-期末考试试卷A-工程073，2.docVIP

3 Engineering Mechanics（A卷） 工程081-2班；工设081-2；建环081-3 15 01 2010 一Determine the following questions true or false (Two marks for each question, total marks twenty). 判断题 （每题2分，共20分） centers should be on a common straight line for the equilibrium equations of the coplanar force system 平面一般力系平衡时，应用三矩式方程需附加三矩心在一条直线上。（× ） 2．Normally there are six equilibrium equations for three dimensional force system, then at least six independent unknowns can be determined. 空间任意力系可以列出六个平衡方程，求出六个独立的未知量。（( ） 3．Two straight bars made by different materials with same length and area of cross section, exerted by same axial forces; then the stresses on the cross sections of the bars are identical, but the strength and total deformation values different. 两根长度﹑横截面积相同，但材料不相同的等截面直杆，当它们承受相同的轴力时，则两杆在横截面上的应力相等，但两杆的强度和总变形不相等。（(） 4．When a circle shaft is twisted, there are only shear stresses perpendicular to radius, nor normal stresses, the maximum of shear stresses happen on the surface of the shaft. 圆轴扭转时横截面上只有垂直于半径方向的切应力而没有正应力，最大应力发生在表面处。（ ( ） 5．Comparing with the solid and hollow shafts with same areas of cross section and gravity, there is more strength for the solid one. 比较材料横截面积和重量都相同的实心圆轴和空心圆轴，实心圆轴的强度高。（ × ） 6．There are only normal stresses at the cross sections for the pure bending, and the maximum are distributed on the upper and lower edges of cross sections. 纯弯曲时在梁的横截面上只有正应力，最大正应力发生在横截面的上下边沿点处。（ ( ） 7．There are not only normal stresses, but also shear stresses at the cross sections for the lateral bending, and the maximum of shear stresses are distributed on the neutral axis. 横力弯曲时在梁的横截面上既有正应力﹑又有切应力；最大切应力发生在横截面的中性轴上。（ ( ） σ3 2．Find out the principle stresses of element in the Figure as below, and draw t