Engineering Mechanics Questions and Answers - Equilibrium in Three Dimensions

1. A force is developed by a support that not allows the ________ of its attached member.
a) Translation
b) Rotation
c) Addition
d) Subtraction

Answer: a
Explanation: The force developed by a support doesn’t allow the translation of its attached member. This is the basic condition for the equilibrium of the forces in any dimension. This rule is applied when the support reactions are taken into the account for the equilibrium of the body.

2. A couple moment is developed when _______ of the attached member is prevented.
a) Translation
b) Rotation
c) Addition
d) Subtraction

Answer: b
Explanation: The development of the couple moment is when there is a prevention of the rotation of the attached member. This is the basic condition for the equilibrium of the couple moments in any dimension. This rule is applied when the couple moments are taken into the account for the equilibrium of the body.

3. We first make equilibrium equations of the body by considering all the three dimensional forces and then the free body diagram is made and solved.
a) The first part of the statement is false and other part is true
b) The first part of the statement is false and other part is false too
c) The first part of the statement is true and other part is false
d) The first part of the statement is true and other part is true too

Answer: d
Explanation: We first make the free body diagram and then we make the equilibrium equations to satisfy the given conditions. This helps us to solve the question easily. As this reduces the part of imagination and increases accuracy too.

4. ∑Fx=0, ∑Fy=0 and ∑Fz=0 are vector equations for the three dimensions. They are satisfied when the body is achieved its state of equilibrium.
a) True
b) False

Answer: b
Explanation: The answer is false as the equations asked are scalars. As we make the net sum of the forces along the axis equal to zero. Of course this equation comes from the solving the vector forms, but still the result is a scalar, hence the equations are scalar.

5.The supports in the 3D are having more than three reaction forces. Because they are having three axis on which the components of the forces need to be zero.
a) The first part of the statement is false and other part is true
b) The first part of the statement is false and other part is false too
c) The first part of the statement is true and other part is false
d) The first part of the statement is true and other part is true too

Answer: d
Explanation: As 3D is defined as the three axis system, we have to consider the equilibrium in all the three axis. This will make the equilibrium go on all the axis of the 3D space. And hence will cancel all the forces

6. The single pin, single bearing and single hinge resist _______
a) Force
b) Couple moments
c) Both force and couple moments
d) Inertia

Answer: c
Explanation: The experiments have founded that the single pin, single bearing and single hinge resist both force and couple moments. This does helps in attaining the equilibrium of the body. Thus proper guiding must be taken during solving the question on the same.

7. If the supports are properly aligned then the reaction forces developed are adequate to support the body.
a) Statement is true only in 2D
b) Statement is true only in 3D
c) Statement is true throughout
d) Statement is true only in 1D

Answer: c
Explanation: This is the basic nature observed during the experiments on the beams an all the support system. The dimension doesn’t affect the equilibrium conditions. The main motto is to achieve the equilibrium. It is achieved by equating the net force equal to zero.

8. If the supports are not properly aligned then the reaction forces developed are adequate to support the body.
a) Statement is true only in 2D
b) Statement is true only in 3D
c) Statement is false throughout
d) Statement is true only in 1D

Answer: c
Explanation: This is the basic nature observed during the experiments on the beams an all the support system. The dimension doesn’t affect the equilibrium conditions. The main motto is to achieve the equilibrium. It is achieved by equating the net force equal to zero. But here the system is not properly aligned.

9. To satisfy the conditions of the equilibrium, the must not only be having a net force zero, but also be properly held or constrained on its supports.
a) True
b) False

Answer: a
Explanation: To satisfy the conditions of the equilibrium, the must not only be having a net force zero, but also be properly held or constrained on its supports. The more the stable are the supports the more the stable is the equilibrium, that is the more easily is the equilibrium is achived.

10. What is redundant support?
a) The supports consisting of hinge and a roller
b) The supports consisting of hinge only
c) The supports consisting of roller only
d) The supports more than necessary to hold the structure

Answer: d
Explanation: The supports if are more than the supports required to hold the structure are termed as the reductant supports. It becomes statically indeterminate. This not only creates a problem in achieving the equilibrium but also affects the calculation of the equilibrium.