Engineering Mechanics(Northwestern Polytechnical University) 中国大学mooc慕课答案2024版 m67369

工程力学（西北工业大学）

Chapter1 ： Axioms of Statics and Freebody Diagram Ch1 Free body diagram

1、

答案: b

2、

答案: C

3、

答案: D

4、

答案: C

5、

答案: D

6、

答案: D

7、

答案: B

8、

答案: C

Chapter 2 ： Coplanar Fundamental Force Systems Ch2 Fundmental Force system

1、

答案: C

2、

答案: B

3、

答案: D

4、

答案: A

5、

答案: C

6、

答案: B

7、

答案: C

8、

答案: D

9、

答案: D

10、

答案: A

11、

答案: C;
D

12、

答案: A;
D

Chapter 3： General Coplanar Force System Ch 3： General Coplanar Force System

1、

答案: C

2、

答案: D

3、

答案: A force passing by point O

4、

答案: A force couple

5、

答案: D

6、

答案: FBC=245.24N

7、

答案: A

8、

答案: B

9、

答案: C

10、

答案: A

11、

答案: A

12、

答案: D

13、

答案: 884.5N;
FAx=736N,  FAy=490.5N

Chapter 4 Equilibrium of a Body System Ch4 Equilibrium of a Body System

1、

答案: C

2、

答案: 250N

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,

3、

答案: A

4、

答案: B

5、

答案: B

6、

答案: 15kN

7、

答案: 40kN

8、

答案: FCx=F，FCy=F

9、

答案: MA＝12kN·m

10、

答案: Fcx=F，Fcy=F

Chapter 5 Friction Ch5 Friction

1、

答案: Keep static.

2、

答案: Sliding. 

3、

答案: A is sliding. B keep static.

4、

答案: Keep static.

Chapter 6 Introduction to Mechanics of Materials

1、 Strength, stiffness and stability of members (          ).

答案: Related to the mechanical properties of materials and the shape, size of members.

2、 In the following discussion about the internal force and stress, (         ) is correct.

答案: The stress is the intensity of the internal force.

3、 When we study the equilibrium of a member or a part of it, we can use the original sizes before deformation to analyze, that because we adopt the (           ).

答案: Limitation of small deformation;

4、 The internal force on a cross section can usually be simplified as (         ).

答案: A principal vector and a principal moment;

5、 In the following conclusions, (        ) is wrong.

答案: If the object displaces, it must deform at the same time.

Chapter 7 Axial Tension and Compression

1、  As shown in the figure, two deformation measuring instruments are respectively installed at A and B of the tensile test specimen, the magnification is respectively  and . The gauge length is s = 20 mm, and the reading increment of the measuring instrument after tension is , . Then the Poisson’s ratio μ of this material is (          ).

答案:  1/3; 

2、 For the simple crane shown in the figure, BC is a steel bar and AB is a wood bar. The cross-sectional area of AB is , allowable normal stress ; the cross-sectional area of BC is Ast =6 cm2,  allowable normal stress. Then the allowable lifting weight F  is (     ).

答案: 40.5kN;

3、 There are three concentrated forces are applied at the bar, as shown in the figure. The axial force on section m-m is (      ).

答案:  .

4、 A stepped bar is shown in the figure, segment AB is made of steel and segment BD is made of aluminum. With the external forces F, (       ).

答案: for the three segments they have the same axial force.

5、 Two bars with different cross-sections, one is circular and another is rectangular. If the two bars have the same materials, areas but different lengths, with the same external forces as shown in the figure, for the two bars (     ) are different.  

答案: axial normal stress σ ;

6、 The bar shown in the figure is subjected to four equal axial external forces. In segment (       ) the deformation is zero.

答案: BC .

Chapter 8 Shear

1、 The pin passes through the circular hole on the flat plate and is subjected to a pull force F at its lower end. The areas of the shear plane and bearing plane of the pin are respectively (       ).

答案: ;

2、  The relation of the three elastic constants E, G, μ of isotropic materials is (        ).

答案:  ;

3、  For connecting members, shear plane and bearing plane are (        ).

答案: Respectively parallel and perpendicular to the direction of external forces

4、 The rivet connection is shown in the figure, and the bearing stress of the rivet is (        ).

答案:  ;

5、 For the two states of stress of units a and b, (       ) .

答案:  a is correct;

Chapter 9 Torsion

1、 A hollow circular shaft with the ratio of inner and outer diameters α = d / D, if the maximum shear stress on the cross section is τ when the two ends are subjected to the torsional couple moments, then there are four answers to the shear stress at the inner circumference, the correct one is (     ).

答案: ;

2、  The prismatic transmission shaft is shown in the figure. Wheels B and D are driving wheels and wheels A, C ,E are driven wheels. If the input powers on driving wheels B and D are equal, the output powers on driven wheels A, C and E are equal too, and if only torsional deformation is considered and bending deformation is not considered, the position of dangerous section is (    ).

答案:  In segment AB and segment DE.

3、 As shown in the figure, the circular shaft is made of steel and copper by welding. If it is acted by an external couple, the copper part and the steel part are the same in (    ).

答案: Shear stress in torsion;

4、 For a solid circular shaft and a hollow circular shaft, if they have the same material, cross-sectional area, length and are subjected to the same external torques, there are four answers to the relation between the torsional angles of the two shafts, the correct one is (        ).

答案:

5、 If the diameter of the torsional solid circular shaft is doubled, its rigidity is 8 times of the original one.

答案: 错误

Chapter 10 Internal Forces in Bending

1、 In the following figures, figure (    ) shows that the bending moment M on the section is positive and the shear force   is negative .

答案:

2、  If the bending moment M on the beam segment is a linear function of x, the function of shear force is (     ).

答案: Constant;

3、 For plane bending the characteristics of deformation are (    ).

答案: The axis after deformation is in the same plane with the loading plane.

4、 As shown in the figure, the cantilever beam is subjected to a uniformly distributed load. In the following conclusions, (   ) is wrong.

答案: The bending moment in segment AB is constant.

5、 The cantilever beam and the simply supported beam are equal in length, they have (     ).

答案: The same bending moment diagrams and the same shear force diagrams;

Appendix A Moments of Areas Appendix A Moments of Areas

1、 If the section figure has a symmetry axis, then for the figure (    ) to its symmetry axis.

答案: The static moment of inertia is zero, the moment of inertia is not zero.

2、 The area of the graph is A , the  axis pass through the centroid C and parallel to the  axis, the distance between  axis and the  axis is . It is known that the moment of inertia of the graph with respect to  axis is , and the moment of inertia of the graph with respect to  axis is (     ).

答案: ;

3、  Let the moment of inertia of the rectangle to its symmetric axis Z is I. When the ratio of length to width remains unchanged and the area is doubled, the moment of inertia of the rectangle to its symmetric axis Z will become (     ).

答案: 4I ;

4、 For the figure as shown, if the centroidal axis Z divides the figure into two parts, then ( ) must be established.

答案:

5、 In the geometric properties of planes, the values of static moment of inertia and moment of inertia can be positive, negative and zero.

答案: 错误

Chapter 11 Stresses in Bending

1、 In the following cases, (    ) belongs to pure bending.

答案: There is no shear force on each cross section of the member, and the bending moment is a constant.

2、 The forces on the cantilever beam are shown in the figure, (       ).

答案: Pure bending occurs in segment AB and transverse bending occurs in segment BC;

3、 The cantilever beam with T-section subjected the force as shown in the figure, where   axis passes through the centroid of the cross section, which is (      ) of the cross section of the beam.

答案: The neutral axis is  axis, and the maximum tensile stress is at the lower edge of the beam;

4、 When the beam with rectangular section is bent, in the neutral axis of the cross section (     ).

答案: Shear stresses are maximum, normal stresses are zero;

5、 As shown in the figure, the cantilever beam with constant section is subjected to a concentrated force and a concentrated couple. If the maximum normal stress and the maximum shear stress at cross section C are σ and τ respectively, the maximum normal stress and the maximum shear stress at cross section A are (     ).

答案: 0 and τ .

Chapter 12 Deflection of Beams

1、 For two beams with same length , flexure rigidity EI and bending internal force diagrams, in the same coordinate system the beams (     ).

答案: Have different deflection equations but same curvature equations;

2、 The cantilever beam is subjected to external forces as shown in the figure, on cross section B (      ).

答案: Both the deflection and the angle of rotation are zero.

3、 For two cantilever beams with same length, loading form, flexural rigidity EI but different cross-section, they have (      ).

答案: Different maximum normal stress but same maximum deflection;

4、 For the approximate differential equation of the deflection curve , the approximation is shown in (       ).

答案: With  instead of 1/ρ and the effect of the shear force to deformation is omitted.

5、 The condition for the existence of the approximate differential equation of deflection curve is (     ).

答案: Meet the above conditions at the same time.

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