# Engineering Mechanics Questions and Answers – Moment of Inertia for Composite Areas

This set of Tough Engineering Mechanics Questions and Answers focuses on “Moment of Inertia for Composite Areas”.

1. Composite materials are of no use for any engineers.
a) False
b) True

Explanation: The composite materials are of much importance to the chemical engineer. This means that the composite materials are variedly used in the chemical industries. It can be used in the bridges made for the pipelines, etc.

2. What is not the condition for the equilibrium in three dimensional system of axis for the composite bodies if we are determining the moment of inertia for them?
a) ∑Fx=0
b) ∑Fy=0
c) ∑Fz=0
d) ∑F≠0

Explanation: For the equilibrium in the three dimensional system of axis we have all the conditions true as, ∑Fx=0, ∑Fy=0 and ∑Fz=0. Also, we have the summation of the forces equal to zero. Which is not a non-zero value.

3. We sometimes use the moment caused by the force so as to determine the moment of inertia of the body. The moment is the cross product of which two vectors?

Explanation: The cross product needs to take in the proper sequence. If not taken then the answer is just the opposite of the true answer. That’s why, the answer is not the Force and Radius vectors, but the Radius and Force vectors. Because the moment has its direction, as many of the cross products have, and thus precaution needs to be taken.

4. Determine the moment of area of the area below about x-axis.

a) 101 x 106 mm4
b) 1 x 106 mm4
c) 10 x 106 mm4
d) 15 x 106 mm4

Explanation: The product of the centroid of the section to its mass to the total mass of the body is the centre of mass. Thus the answer. The ratio is generally used to locate the coordinate of the centroid or the centre of mass.

5. Composite materials can be of __________ shapes for the determination of the moment of composite areas.
a) Any
b) Circular only
c) Rectangular only
d) Oval only

Explanation: The composite materials can be of any shape. This means that the shape of the material can be varied. Thus any shape can be imparted to the composite materials and then be used in the industries variedly.
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6. If any external force also is applied on the distributed loading on which the moment of inertia is to be determined on the composite body then?
a) The net force will act at the centroid of the structure only
b) The net load will not be formed as all the forces will be cancelled
c) The net force will act on the base of the loading horizontally
d) The net force will not be considered, there would be a net force of the distribution, and rest will be the external forces

Explanation: The external forces are treated differently. They are not added by the force of the distributed loading. That is the force not only acts at the centroid always. It can be shifted also. Depending on the external forces. Thus the use of centroid or centre of mass.

7. Determine the moment of area of the area below its centroid axis.

a) 28.125 x 106 mm4
b) 1 x 106 mm4
c) 10 x 106 mm4
d) 17 x 106 mm4

Explanation: The product of the centroid of the section to its mass to the total mass of the body is the centre of mass. Thus the answer. The ratio is generally used to locate the coordinate of the centroid or the centre of mass.

8. Two of the things of the composite materials are to be known so that their moment of inertia can be varied. Which of the following is one of them?
a) Weight of the centre of gravity
b) Weight of the body
c) Location of the centroid of gravity
d) Location of the centre of mass

Explanation: The centre of the gravity’s location and the weight of the composite body is needed to be known. This means that if both of the quantities of the composite body is known then the moment of inertia of the body can be altered. Thus both are very important things to be known about the composite bodies.

9. The number of a particle does affect the moment of inertia. A composite body is consisted of __________ number of particles.
a) Infinite
b) Finite
c) Hundreds
d) Thousands

Explanation: The various bodies are composed of an infinite number of particles. They are very small in size. They can’t be seen by our naked eyes. Thus the number of particles is not thousands nor hundreds. But it is uncountable.

10. We use sometimes the measures to know the direction of moment of inertia. It is done by right handed coordinate system. Which is right about it for the composite bodies (consider the mentioned axis to be positive)?
a) Thumb is z-axis, fingers curled from x-axis to y-axis
b) Thumb is x-axis, fingers curled from z-axis to y-axis
c) Thumb is y-axis, fingers curled from x-axis to z-axis
d) Thumb is z-axis, fingers curled from y-axis to x-axis

Explanation: As right handed coordinate system means that you are curling your fingers from positive x-axis towards y-axis and the thumb which is projected is pointed to the positive z-axis. Thus visualizing the same and knowing the basic members of axis will not create many problems.

11. We often use the centre of mass of the composite area to calculate the moment of inertia. The centre of mass for these composite body is the ratio of ________ to _________
a) The product of centroid and mass to the total weight
b) The addition of centroid and weight to the total weight
c) The subtraction of centroid and weight to the total weight
d) The product of centroid and mass to the total mass

Explanation: The product of the centroid of the section to its mass to the total mass of the body is the centre of mass. Thus the answer. The ratio is generally used to locate the coordinate of the centroid or the centre of mass.

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