# Engineering Mechanics Questions and Answers – Centre of Gravity

This set of Engineering Mechanics Multiple Choice Questions & Answers (MCQs) focuses on “Centre of Gravity”.

1. A 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.

2. A body’s all small particles have a small weight which is being applied by them to the body, which adds up to the total weight of the body.
a) True
b) False

Explanation: The weight of the body is the sum of all the small weights that are been applied by all the particles. The smaller the particle the smaller the weight it applies. Thus the total weight of the body is the summation of all the infinite number of small weights applied to the body.

3. The all small weights that are being applied by all the infinite particles of the body act __________ to each other.
a) Parallel
b) Perpendicular
c) Collinear
d) Divergent

Explanation: All the small weights that are being applied by all the particles are being applied by them parallel to themselves. Thus the parallel is the right answer. Thus the total sum of all these small weights adds up to the total weight of the body.

4. The total of all the weights of small particles adds up to give the total body weight. This weight is the force vector which is being passed by ________
a) Axis of rotation
b) Axis of rolling
c) Centre of Gravity
d) Centre of mass

Explanation: The total body weight always passes through the centre of gravity. All the forces are parallel is the right answer. Thus the total sum of all these small weights add up to the total weight of the body. Which passes through the centre of gravity.

5. The centre of gravity is the ratio of ________ to _________
a) The product of centroid and weight 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 weight to the total mass

Explanation: The product of the centroid of the section to its weight to the total weight of the body is the centre of gravity. Thus the answer. The ratio is generally used to locate the coordinate of the centroid or the centre of gravity.
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6. The x axis coordinate and the y axis coordinate of the centre of gravity are having different types of calculations to calculate them.
a) True
b) False

Explanation: The calculation is general to all the axis of the coordinate system. This means that the calculations are generalised for all the axis. And it is the product of the centroid of the section to its mass to the total weight of the body is the centre of gravity.

7. The centre of mass 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.

8. The centre of volume 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 volume to the total weight
d) The product of centroid and volume to the total volume

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

9. Determine the y coordinate of centroid of the line in the shape of parabola as shown.

a) 0.514m
b) 1.410m
c) 2.410m
d) 0.10m

Explanation: The weight of the body is the sum of all the small weights that are been applied by all the particles. The smaller the particle the smaller the weight it applies. Thus the total weight of the body is the summation of all the infinite number of small weights applied to the body.

10. Volume is best given by ___________
a) Product of mass and density
b) Ratio of mass to density
c) Addition of mass and density
d) Subtraction of mass and density

Explanation: The density is the ration of the mass to the volume of the body. Thus arranging them and the volume is said to be a ratio of mass to density. This equation is generally used in the calculations of the centroid of the body or the centre of gravity.

11. We use sometimes the measures to know the direction of moment. It is done by right handed coordinate system. Which is right about it(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.

12. If A is any vector with Ai + Bj + Ck then what is the y-axis component of the vector if we are using the vector math to calculate the centre of gravity?
a) B units
b) A units
c) C units
d) Square root of a sum of squares of the three, i.e. A, B and C

Explanation: As the given vector is shown in the Cartesian system, the number with “j” is the Y-axis component of the given vector. With the numbers with “i” representing components of x-axis and “k” representing the z axis respectively.

13. If the force vector F acting along the centre of gravity is having its x-axis component being equal to Z N, y-axis component be X N and z-axis component be Y N then vector F is best represented by?
a) Xi + Yj + Zk
b) Yi + Xj + Zk
c) Zi + Yj + Xk
d) Zi + Xj + Yk

Explanation: It is given that x, y and z-axis components are Z, X and Y respectively. Thus, just by placing the right coordinates we get option d to be correct. Here just the interchange of the axis’s represented with their respective axis is creating confusion. Which must be figured out.

14. Which statement is right for force acting by the small particles of the body having it’s vector form as = Ai + Bj + Ck?
a) In rectangular components representation of any vector we have vector F = Ai + Bj + Ck
b) In rectangular components representation of any vector we have vector F = Ax + By + Cz
c) In rectangular components representation of any vector we have vector F = Fx + Fy + Fz
d) In rectangular components representation of any vector we have vector F = Fi + Fj + Fk

Explanation: As given the vector is F = Ai + Bj + Ck, this implies that the x, y and z-axis components of this vector is A, B and C respectively. But, in rectangular components representation of any vector, the vector is written as F = Fx + Fy + Fz.

15. Determine the x coordinate of centroid of the line in the shape of a parabola as shown.

a) 0.410m
b) 1.410m
c) 2.410m
d) 0.10m

Explanation: The weight of the body is the sum of all the small weights that are been applied by all the particles. The smaller the particle the smaller the weight it applies. Thus the total weight of the body is the summation of all the infinite number of small weights applied to the body.

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