# Engineering Mechanics Questions and Answers – Bending Moment Diagram

This set of Engineering Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Bending Moment Diagram”.

1. Which of the following is correct in bending moment diagram w.r.t the moment (M) of the force (F) acting on the body at a distance L from the axis of the rotation?
a) M=FLsinθ
b) M=FLcosθ
c) M=F.Lsinθ
d) M=FxLsinθ

Explanation: The moment of the force about the axis of rotation by the application of the force on the body is given by the cross product of both. If the force not perpendicular to the axis, and making angle θ then cosine form of angle is used. As usually used in the cross product.

2. What does the moment of the force measure in the bending moment diagram?
a) The tendency of rotation of the body along with an axis
b) The moment of inertia of the body about any axis
c) The couple moment produce by the single force acting on the body
d) The total work done on the body by the force

Explanation: The moment of the force measures the tendency of the rotation of the body along any axis, whether it be the centroid axis of the body or any of the outside axis. The couple moment is produced by two forces, not by a single force. The total work done is the dot product of force and distance not the cross.

3. Determine the moment’s magnitude produced by the force as shown in the diagram, which tends to rotate the rod ORQP along QP.

a) 80.49 Nm
b) 72.12 Nm
c) -36.67 Nm
d) 36.67 Nm

Explanation: The use of the formula A.(rxF) gives the answer. In which A is 0.89i + 0.447j m. And the force is 300N, which is being applied at the end of the rod. Thus, after finding the equation of the axis and then replacing it in the equation shown above we get the answer. Actually, the main task is to know the axis equation in the vector form. Then get the magnitude of the moment.

4. The moment of the force in bending moment diagram is the product of the force and the perpendicular distance of the axis and the point of action of the force.
a) True
b) False

Explanation: The moment is the product of the force applied to the body and the perpendicular distance of the point of action of the force to the axis about which the body is being rotated. That is the moment is the cross product of the force and the distance between the axis and the point of action.

5. If any force is applied in the direction of the positive x-axis, and there are three different points in bending moment diagram on which the moment of this force is to be calculated. Then if these three points are on the positive side of the y-axis with varying distance, then what will be the direction of the moment caused by the force to the individual point?
a) Towards positive z-axis
b) Towards positive y-axis
c) Towards positive x-axis
d) Towards negative z-axis

Explanation: If you will apply the right hand rule on the system given then the right answer is the positive z-axis. Which is because the force is lying on the x-axis and is heading towards the positive infinity of the x-axis. And the points are in the positive y-axis. Apply the rule, and get the direction.

6. Determine the moment of the force F along the segment QP of the pipe assembly shown in the figure.

a) 110Nm
b) 100Nm
c) 500Nm
d) 510Nm

Explanation: The use of the formula A.(rxF) gives the answer. In which A is 0.6i + 0.8j m and the r is 0.5i + 0.5k. And the force is 300N, which is being applied at the end of the rod. Thus, after finding the equation of the axis and then replacing it in the equation shown above we get the answer. Actually, the main task is to know the axis equation in the vector form. Then get the magnitude of the moment.

7. Which of the following is true for bending moment diagram?
a) Total moment of various forces acting on the body is the vector sum of all moments
b) Total moment of various forces acting on the body is the algebraic sum of all moments
c) Total moment of various forces acting on the body is always zero
d) Total moment of various forces acting on the body is the vector sum of all moments which is perpendicular to each other forces

Explanation: The moment is the vector quantity. Thus the value of the total moment caused by various forces acting on the body is the vector sum of all the vectors. Also, the moments are not perpendicular to each other, unless it is specified. Thus assumptions cant be taken for the direction of the moment.

8. If you are getting to know about the direction of the moment caused by the force applied on the body by using your wrist and curling it in the direction of the rotation then which of the following is not right for bending moment diagram?
a) The thumb represents the direction of the force
b) The thumb represents the direction of the moment
c) The fingers represents the direction of the force
d) The direction in which you curl your wrist is towards the direction of the distance from point of contact of force to the axis of rotation.

Explanation: The curled hand represents a various thing. The direction of the moment axis is given by the thumb. The direction of the force is given by the fingers. As we place the fingers on the force and curl towards the rotational direction of the body about the axis.

9. If the rotation is clockwise in this page, suppose, then in which direction will the thumb project if you curl your hand in the same direction of the rotation for bending moment diagram?
a) It will point to the direction perpendicular to the plane of the paper and towards you
b) It will point to the direction perpendicular to the plane of the paper and away from you
c) It will point to the direction parallel to the plane of the paper and towards right
d) It will point to the direction parallel to the plane of the paper and towards left

Explanation: As the curling will give the direction perpendicular to the paper. But it does depend upon the rotation sense. In this example, the sense is clockwise. Thus the thumb goes into the paper. That is it goes away from the viewer. Thus the answer.

10. The tendency of rotation of the body along any axis in the bending moment diagram is also called ___________
a) Moment of inertia
b) Moment of couple
c) Torque
d) Force

Explanation: The tendency of rotation of the body along any axis also called the torque. It is the moment of the force acting perpendicular to the direction of the axis of rotation. If the axis and the force are meeting at any point then there is no moment applied by the force.

11. What does FLsinθ mean/represents in bending moment diagram for the moment (M) of the force (F) acting on the body at a distance L from the axis of the rotation?
a) The direction vector of the moment
b) Unit vector of the moment vector
c) The magnitude of the moment caused by the force on the body
d) The perpendicular distance of the force from the axis of rotation

Explanation: The moment of the force about the axis of rotation by the application of the force on the body is given by the cross product of both. If the force not perpendicular to the axis, and making angle θ then cosine form of angle is used. Thus, FLsinθ represents the magnitude of the moment.

12. The moment axis, force and the perpendicular distance in the bending moment diagram is lying in____________
a) Two planes perpendicular to each other
b) A single plane in the direction of the force
c) A single plane in the direction of the perpendicular distance
d) A single line in the direction of the force

Explanation: The moment axis, force and the perpendicular distance is lying in the three dimensional Cartesian. It doesn’t lye on the single plane. It also doesn’t lye in a single line. Nor in the direction of the force. Thus they all lye in the planes which are perpendicular to each other.

13. If a force applied at any point in its line of action and is still creating the same moment about any fixed point say P, then the force is said to be a sliding vector. What is the name of this property in a bending moment diagram?
a) Associative property
b) Distributive property
c) Negative associative property
d) Principle transmissibility of the force

Explanation: If a force applied at any point in its line of action and is still creating the same moment about any fixed point say P, then the force is said to be sliding vector. This is because the moment of the force which is acting on its line of axis at the point P is same throughout. This is known as the principle transmissibility of the force.

14. The basic way of getting the direction of the moment caused by the force in a bending moment diagram is:
a) The use of left hand rule with thumb giving the direction of the moment
b) The use of right hand rule with thumb giving the direction of the moment
c) The use of right hand rule with forefinger giving the direction of the moment
d) The use of left hand rule with forefinger giving the direction of the moment

Explanation: The basic way of doing so is to use right hand rule and not the left hand rule. The direction of the moment axis is given by the thumb. The direction of the force is given by the fingers. As we place the fingers on the force and curl towards the rotational direction of the body about the axis.

15. If a force applied at any point in its line of action and is still creating the same moment about any fixed point say P, then the force in bending moment diagram is said to be______________
a) Couple
b) Sliding vector
c) Slider couple
d) Couple slider

Explanation: If a force applied at any point in its line of action and is still creating the same moment about any fixed point say P, then the force is said to be a sliding vector. This is because the moment of the force which is acting on its line of the axis at the point P is the same throughout. Whatever be the direction of the distance.

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