# Engineering Mechanics Questions and Answers – Internal Forces Developed in Structural Members – 2

This set of Engineering Mechanics Multiple Choice Questions & Answers focuses on “Internal Forces Developed in Structural Members – 2”.

1. The ____________ forces are used are used in the method of sections for the calculation of the internal forces.
a) Internal rotational
b) Couple rotational
c) Translational
d) External

Explanation: The calculations of the method of sections involve the making of the free diagrams and then use external forces to determine the internal forces. Design so as to withstand the loads which are going to be added to the beams. Thus the loads which are being added externally are being used in the free body diagrams.

2. Every point on the force vector which is the internal force is having the same magnitude and the same direction as the whole force vector have.
a) True
b) False

Explanation: The vector is made by joining the final and the starting point of the internal force. If we consider any arbitrary point then the length would be calculated w.r.t the starting point, which might give different magnitude but same direction. Thus the answer is false.

3. For getting the normal force on the supports, we do what?
a) Make the vertical sum of the forces equal to zero
b) Make the horizontal sum of the forces equal to zero
c) Make the moment sum of the forces equal to zero
d) Make the rotational sum of the forces equal to zero

Explanation: The making of the vertical force sum zero makes the normal force to be determined. This means that the equilibrium equations when applied at the support give us the answer. Hence the determination of the normal force is done easily by equating the vertical force sum equal to zero.

4. For getting the horizontal component of the support reactions what do we do?
a) Make the vertical sum of the forces equal to zero
b) Make the horizontal sum of the forces equal to zero
c) Make the moment sum of the forces equal to zero
d) Make the rotational sum of the forces equal to zero

Explanation: The making of the horizontal force sum zero makes the horizontal force to be determined. This means that the equilibrium equations when applied at the support give us the answer. Hence the determination of the horizontal force is done easily by equating the horizontal force sum equal to zero.

5. Twisting moment is also called as __________
a) Moment of line
b) Moment of section
c) Moment of plane
d) Torsional moment

Explanation: The twisting moment is applied at the point where the couple moment is being applied or is made by the external forces. This makes the formation of the twisting moment along the beam or the torsional moment. Thus the name twisting or the torsional moment.
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a) Centroid
b) Symmetrical centre
c) Rotational centre
d) Chiral centre

Explanation: The loads generally are applied on the centroid of the body. The moment of the body is also calculated along the centroid axis, thus the forces which are acting externally are always acting upon the centroid of the body. Gravity too is acted upon the centroid of the body.

7. The area of does make the difference in the internal forces, that is if the area is large the internal force acting is also large and vice versa.
a) True
b) False

Explanation: This is because the internal forces are independent of the area. They are applied irrespective of the area given to the beams. They are dependent on the external forces. The more the external forces, the more are the internal force. That is the more is the amount of the internal forces.

8. The magnitude of each loading will be ___________ at various points along the axis of the member of the beam.
a) Same
b) Different
c) Slightly different
d) Slightly same

Explanation: The magnitude of each loading will be different on the different points of the beams. The method of section is used to determine these forces. These forces are used so as to make the beams. That is the designing of the beams, the more are the forces than the stronger material is used for the making of the beams.

9. Torsional moment is applied at the ___________ part of the beam.
a) The centroid
b) The left end
c) The right end
d) The axis beyond the body of the beam

Explanation: The torsional moment as said is made to be drawn at the centre of the beam. As it is generated by the various external forces, thus the centroid is the main point of the action of the various forces. Thus the forces which are made to be fallen on the body is having its effect over the centroid of the beam.

10. Normal force is equal to _______________
a) The net horizontal force
b) The net vertical force with a negative sign
c) The net horizontal force with a negative sign
d) The net vertical force

Explanation: The normal force is determined by equating the vertical forces equal to zero. This makes the vertical forces to go on the other side of the equation. Suppose the L.H.S. is having the sum of the vertical forces then the R.H.S. is having the term normal force. That is the normal force is being equated to the negative of the sum of vertical forces.

11. If the normal force creates a tension then the force is said to be ____________
a) Positive
b) Negative
c) Rotational
d) Collinear

Explanation: If the normal forces are giving tension to the body of the beam then the forces are said to be positive. That is if the normal force is making the tension to develop in the beam then it is considered to be positive. This is the basic sign convection that is being used to make the calculations easy.

12. If the shear force creates a clockwise rotation then the force is said to be ____________
a) Positive
b) Negative
c) Rotational
d) Collinear

Explanation: If the shear forces are giving clockwise rotation to the body of the beam then the forces are said to be positive. That is if the shear force is making the beam to develop in the forces that tend to rotate it clockwise then it is considered to be positive. This is the basic sign convection that is being used to make the calculations easy.

13. If the bending of the beam is concave upwards then the bending moment developed is called __________ moment.
a) Positive
b) Negative
c) Rotational
d) Collinear

Explanation: If the bending moment is giving concave bending upward to the body of the beam then the moment are said to be positive. That is if the bending moment is making the beam to develop in the forces that tend to bend the beam concave upward then it is considered to be positive. This is the basic sign convection that is being used to make the calculations easy.

14. In the diagram given below, coordinates of D is (1, -2, 2), C (-2, 0, 0) and B are as shown. The dark region is the cables holding the weight of 600N at origin. Find the tension in the AD section.

a) 900N
b) 693N
c) 646N
d) 0N

Explanation: As the system is in equilibrium so we need to balance the forces. So when apply the condition of net force to be zero in the z direction, we get (2/3)FAD = 600N. This gives us force along AD be 900N.

15. Find the tension in the cable AC.

a) 23.6N
b) 55N
c) 89N
d) -29N

Explanation: First represent the forces in their vector form. Then equate the net sum of the forces in the x, y and z directions to be zero. You will get FB = FC and 2(.848) = 40N. This gives the answer as 23.6N.

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