MECHANICS OF STRUCTURES-I

Two Marks Question Bank

UNIT-I
FORCES AND STRUCTURAL SYSTEMS

1. Define Engineering Mechanics

Engineering Mechanics is defined as the branch of physical science which deals with the
behaviour of a body at rest or motion under the action of forces.
2. What are the branches of Engineering Mechanics?
1. Rigid body Mechanics
2. Deformable body mechanics (also called strength of materials)
3. Fluid Mechanics
3. What are the branches of Rigid body Mechanics?
1. Statics
2. Dynamics
4. Define statics
Statics is defined as the branch of rigid body mechanics, which deals with the behaviour
of a body when it is at rest.
5. Define Dynamics
Dynamics is defined as the branch of rigid body mechanics which deals with the
behaviour of a body when it is in motion.
6. Distinguish between particle and Rigid body
A body of negligible dimension is called a particle. A large number of particles which
occupy fixed positions with respect to each other both before and after applying a load is
called
Rigid body
7. The Quantity which has only magnitude is called (Ans: Scalar)
8. Vector Quantity has both (Ans: Magnitude and direction)
9. Define Force.
Force is defined as an agent which changes or tends to change the state of rest or of
uniform motion of a body. It represents the push or pull exerted by one body on another.
It is a
vector quantity.
10. What are the characteristics of a force?
1. Magnitude
2. Line of action
3. Direction & angle of inclination
11. State Newton's laws of motion
Newton's first law: Everybody preserves in its state of rest, or of uniform motion in a
straight line, unless it is compelled to change that state by forces impressed there on.
Newton's second law: The acceleration of a particle will be proportional to the force and
will be in the direction of the force (ie. F = ma)
Newton's third law: To every action there is an equal and opposite reaction.

12. State the Principle of transmissibility.

It state that “any force at a point on a rigid body can be transmitted to act at any other
point along its line of action without changing its effect on the rigid body”
13. What is collinear force system?
Force acts on a common line of action.
14. What is like parallel forces?
The parallel force which acts in the same direction are called like parallel forces.
15. What is unlike parallel forces?
The parallel force which acts in the opposite direction are called unlike parallel forces.
19. What is coplanar force system?
In coplanar force system, lines of action of all forces lie on a single plane.
20. What is Non-coplanar (or spatial) force system?
In Non-coplanar (or spatial) force system, lines of action of al forces lie on different
planes
21. What is collinear force system?
In collinear force system, all the forces lie on a single line.
22. What is concurrent force system?
In concurrent force system, lines action of all forces intersects at a point.
23. What is parallel force system?
In parallel force system, lines of action of all forces are parallel to each other.
24. State Newton's law of Gravitation?
It .states that two particles of mass m1 and are m2 mutually attracted with equal and
opposite forces.

25. State the difference between internal and external forces.

External forces: The forces which represent the action of other bodies on the rigid body
considered and which are responsible for the external behaviour of the rigid body are
called as
'External forces'.
Internal forces:
The forces which hold together the forming the rigid body or holding the component
parts together are called as internal forces.
26. Define resultant force?
Resultant force is a single equivalent force which can replace the given force system for
an equivalence of effect
27. State parallelogram law of forces?
It states that "If two forces acting simultaneously on a particle be represented in
magnitude and direction by the two adjacent sides of a parallelogram their resultant may
be
represented magnitude and direction by the diagonal of the parallelogram
which passes through their point of intersection.
28. State triangle law of forces?
It states that "If two forces acting simultaneously on a particle represented in magnitude
and direction by the two sides triangle, taken in order, their resultant may be represented
magnitude and direction by the third side of the triangle, taken opposite order".
29. State polygon law of forces?
It states that "If a number of forces acting simultaneously on a particle be represented in
magnitude and direction, by the sides of a polygon taken in order, then the resultant of all
these
forces may be represented in magnitude and direction, by the closing side of the polygon,
taken
in opposite order".
30. State the principle of resolution?
The algebraic sum of the resolved parts of a number of forces in a given direction is equal
to the resolved part of their resultant in the same direction of their resultant and in the
same
direction.
31. What is the significance of parallelogram law in statics of particles?
Parallelogram law is used to find the resultant of two concurrent coplanar forces It can be
applied by both analytically and graphically.
32. Define equilibrium?
A body is said to be in a state of equilibrium, if the body is either at rest or is moving at a
constant velocity.
33. State Lami's theorem?
It states that, "If three coplanar forces acting at a point be in equilibrium, then each force
is proportional to the sine of the angle between the other two".
P/Sin=Q/sin=R/sin
34. What are the three equations of equilibrium?
1. H=0( = )
The algebraic sum of the horizontal for must be zero.
ie., sum of the left hand side forces must be equal to sum of the right hand side forces.
2. V=0( = )
The algebraic sum of the vertical forces must be zero.
ie. Sum of the upward forces must be equal to sum of the downward forces
3. M=0
The algebraic sum of the moments about a point must be zero
ie., sum of the clockwise moments about a point must be equal to sum of the
anticlockwise moments about the same Point.
35. What is neutral equilibrium?
A body is said to be in neutral equilibrium, if it occupies a new position (also remains at
rest) after slightly displaced from its position of rest..
36. What is Free body diagram?
Its is a sketch of the particle which represents it as being isolated from its surroundings. It
reprsents all the forces acting on it

UNIT II
ANALYSIS OF PLANE TRUSS
1. What is mean by perfect frame?
If a frame is composed of such members, which are just sufficient to keep the
Frame in equilibrium, when the frame is supporting the external load, then the frame
is knownn as perfect frame.
2. What are the different types of frames?
The different types of frame are:
• Perfect frame and
• Imperfect frame.
3. What is mean by Imperfect frame?
A frame in which number of members and number of joints are not given by
n = 2j – 3 is knownn as imperfect frame. This means that number of members in an
Imperfect frame will be either more or less than (2j – 3).
4. What is mean by deficient frame?
If the number of member in a frame are less than (2j -3), then the frame is
known as deficient frame
5. What is mean by redundant frame?
If the number of member in a frame are more than (2j -3), then the frame is
known as deficient frame
6. What are the assumptions made in finding out the forces in a frame?
The assumptions made in finding out the forces in a frame are:
The frame is a perfect frame
The frame carries load at the joints
All the members are pin-joined.
7. What are the reactions of supports of a frame?
The frame are generally supported
(i) on a roller support or
(ii) On a hinged support.
8. How will you Analysis of a frame?
Analysis of a frame consists of
Determinations of the reactions at the supports and
Determination of the forces in the members of the frame
9. What are the methods for Analysis the frame?
Methods of joints,
Methods of sections, and
Graphical method.
10. How method of joints applied to Trusses carrying Horizontal loads.
If a truss carries horizontal loads (with or without vertical loads) hinged at one
end supported on roller at the other end, the support reaction at the roller support end
will be normal. Whereas the support reaction at the hinged end will consist of (i)
horizontal reaction and (ii) vertical reaction
11. How method of joints applied to Trusses carrying inclined loads.
If a truss carries inclined loads hinged at one end supported on roller at the
other end, the support reaction at the roller support end will be normal. Whereas the
support reaction at the hinged end will consist of (i) horizontal reaction and (ii)
vertical reaction
12. What is mean by compressive and tensile force?
The forces in the member will be compressive if the member pushes the joint
to which it is connected whereas the force in the member will be tensile if the
member pulls the joint to which it is connected.
13. How will you determine the forces in a member by method of joints?
While determining forces in a member by methods of joints, the joint should
be selected in such a way that at any time there are only two members, in which the
forces are unknown.

UNIT -III
Properties of Sections
1. Define Centre of Gravity.
Centre of Gravity is an imaginary point at which the entire weight of the body is
assumed to act.
2. Define Centre of mass.
Centre of mass is the point where the entire mass of a body is assumed to be
concentrated.
3. Define Centroid.
Centre of gravity of a plane figure is referred as centroid. Centroid is the point at which
the entire area of the figure is assumed to be concentrated
4. Differentiate centroid and Centre of gravity
Centroid is the geometric property of geometrical figures line, area and volume. Centre
of gravity is the physical property of a body like wire, rod, disc and solids
5. When centroid and centre of mass coincide?
Centroid and centre of mass coincide when the density of the material is uniform
throughout the body.
6. State the methods of determining the centre of gravity?
1. By Geometrical considerations
2. Graphical method
3. Integration method
4. Method of moments
7. Write the expressions to find the co-ordinates of centroid by integration method?
For plane figure X = , Y =
For solid figure, X Y =

8. Write the expressions to find centroid of a composite plane figure?

X = sum of first moment of the area about y axis/Total area
= a1 x1a2x2/a1a2
y = sum of first moment of the area about y axis/Total area
= a1 y1a2y2/a1a2
9. The centre of gravity of an equilateral triangle with each side measuring 'a' is
from
any of the three sides. (Ans: a/2 )
10. State Pappus and Guldinus theorems.
Theorem I: The area of the surface generated by revolving a plane curve about a non
intersecting axis in the plane of the curve is equal to the product of length of the curve
and the
distance travelled by the centroid G of the curve during revolution.
A=L(x )
Theorem II: The volume of the solid generated by revolving a plane area about a non
intersecting axis in its plane is equal to the product of area and length of the path
travelled by
centroid G of the area during revolution.
V=A(x )
11. What is Axis of revolution?
The fixed axis about which a plane curve (may be of an arc, straight line etc.,) or a plane
area is rotated is knownn as axis of revolution
12. Define Axis of Symmetry?
The axis about which similar configuration exist with respect to shape, size and weight
on either side is knownn as axis of symmetry. It may be horizontal, vertical or inclined
13. Define moment of inertia of a body.
Moment of inertia (I) about an axis is the algebraic sum of the products of the elements
of mass and the square of the distance of the respective element of mass from the axis.
14. Define Radius of gyration
Radius of gyration of any Lamina defined as the distance from the elemental parts of the
lamina would about a given axis may be given axis at which all the have to be placed, so
as not
to alter the moment of inertia about the given axis.
Radius of gyration k =
Where I = Moment of inertia
A = Total area of the plane
15. State parallel axis theorem?
Parallel axis theorem states that “ if the moment of inertia of a plane area about an axis
through its centroid be denoted by IG, the moment of inertia of the area about an axis
AB,
parallel to the first and at a distance ‘h’ from the centroid is given by ,
IAB=IG+Ah2
16. State perpendicular axis theorem?
It states that “if IXX and IYY be the moment of inertia of a plane section about two
perpendicular axis meeting at ‘O’ the moment of inertia IZZ about the axis Z-Z
perpendicular to
the plane and passing through the intersection of X-X and Y-Y is given by the relation,
IZZ=IXX+IYY
17. Define polar moment of inertia?
The second moment of area about a pole '0' is called the polar moment of inertia (Ip).
Ip= Ixx+ Iyy
18. Unit of moment of inertia is_ (Ans: mm4 (or) cm4 (or) m4)
19. Radius of gyration of a plane area with respect to X-X axis (Kx) is -------------
20. Radius of gyration of a plane area with respect to Y-Y axis (Ky) is -------------
21. Radius of gyration of a plane area with respect to polar axis (Ko) is ----------
K2x+K2y
22. Mass moment of inertia, Ixx =----------------- (ans:
23. The Radius of gyration of the mass of a body with respect to x-x axis isk =
24. Polar moment of inertia of a circle of diameter, d is ------------------ (ans:
25. Moment of inertia of a rectangle about the base is ---------- times that of through
the
centre of gravity (ans: 4)
26. The product of inertia of a rectangle of a plane figure about XX axis and YY axis
Ixy= -
----------- (Ans:
27. The unit of product of inertia is same as that of ----------------- (Ans: moment of
inertia)
28. Product of inertia of a rectangle about their edges= --------------- (Ans:b2h2/4)
I YEAR 2th SEMESTER)
29. Parallel axis theorem concerning to product of inertia is ------------ (IMN=Ixy+Ax
y)
30. Second moment of area with respect to a set of perpendicular axes is knownn
as-----------
(Ans: Product of inertia)
31. The axes about which the product of inertia is zero are called------- (Ans:
principal axes)
32. Moment of inertia with respect to the principal axes is knownn as------------
(Ans: Principal moment of Inertia)
 UNIT - IV
Elastic Properties of Solids
1. Define stress.
When an external force acts on a body, it undergoes deformation. At the same
time the body resists deformation. The magnitude of the resisting force is numerically
equal to the applied force. This internal resisting force per unit area is called stress.
Stress = Force/Area
When a body is subjected to an external force, there is some change of dimension in the
body. Numerically the strain is equal to the ratio of change in length to the original length
of the body.= P/A unit is N/mm^2
2. Define strain
δ Strain = Change in length/Original length
e = δL/L
3. State Hooke’s law.
It states that when a material is loaded, within its elastic limit, the stress is
directly proportional to the strain.
Stress α Strain
σαe
Where,
σ = Ee
E = σ/e unit is N/mm^2
E - Young’s modulus
σ - Stress
e - Strain
4. Define shear stress and shear strain.
The two equal and opposite force act tangentially on any cross sectional plane of
the body tending to slide one part of the body over the other part. The stress induced is
called shear stress and the corresponding strain is known as shear strain.
5. Define Poisson’s ratio.
When a body is stressed, within its elastic limit, the ratio of lateral strain to the
longitudinal strain is constant for a given material.
Poisson’ ratio (μ or 1/m) = Lateral strain /Longitudinal strain
6. State the relationship between Young’s Modulus and Modulus of Rigidity.
E = 2G (1+1/m)
Where,
E - Young’s Modulus
K - Bulk Modulus
1/m - Poisson’s ratio
7. Define strain energy
Whenever a body is strained, some amount of energy is absorbed in the body. The
energy which is absorbed in the body due to straining effect is known as strain energy.
8. Give the relationship between Bulk Modulus and Young’s Modulus.
E = 3K (1-2/m)
Where,
E - Young’s Modulus
K - Bulk Modulus
1/m - Poisson’s ratio
9. Draw the stress strain Curve for mild steel bar.

10.Draw the stress strain curve for Concrete.

11. Define- elastic limit

Some external force is acting on the body, the body tends to deformation. If the
force is released from the body its regain to the original position. This is called elastic
limit
12. Define – Young’s modulus
The ratio of stress and strain is constant within the elastic limit.
E = Stress
Strain
13. Define Volumetric Stress
The bulk modulus ( K ) describes volumetric elasticity, or the tendency of an object to
deform in all directions when uniformly loaded in all directions
14. Define- lateral strain
When a body is subjected to axial load P. The length of the body is increased. The
axial deformation of the length of the body is called lateral strain.
15. Define- longitudinal strain
The strain right angle to the direction of the applied load is called lateral strain.
16. What is principle of super position?
The resultant deformation of the body is equal to the algebric sum of the
deformation of the individual section. Such principle is called as principle of super
position.
17. Define- Rigidity modulus
The shear stress is directly proportional to shear strain.
N = Shear stress
Shear strain
18. State principle plane.
The planes, which have no shear stress, are known as principal planes. These
Planes carry only normal stresses.
19. Define principle stresses and principle plane.
Principle stress: The magnitude of normal stress, acting on a principal plane is
Known as principal stresses.
Principle plane: The planes which have no shear stress are known as principal
planes.

UNIT 5
Elastic Concepts

1. Define – Young’s modulus

The ratio of stress and strain is constant within the elastic limit.
E = Stress
Strain
2. Define Bulk-modulus
The ratio of direct stress to volumetric strain.
K = Direct stress
V=Volumetric strain
3. Define- Rigidity modulus
The shear stress is directly proportional to shear strain.
N = Shear stress
Shear strain
4. State the relationship between Young’s Modulus and Modulus of Rigidity.
E = 2G (1+1/m)
Where,
E - Young’s Modulus
K - Bulk Modulus
1/m - Poisson’s ratio
5. Define strain energy
Whenever a body is strained, some amount of energy is absorbed in the body. The
energy which is absorbed in the body due to straining effect is known as strain energy.
6. Give the relationship between Bulk Modulus and Young’s Modulus.
E = 3K (1-2/m)
Where,
E - Young’s Modulus
K - Bulk Modulus
1/m - Poisson’s ratio
7. Define Poisson’s ratio.
When a body is stressed, within its elastic limit, the ratio of lateral strain to the
longitudinal strain is constant for a given material.
Poisson’ ratio (μ or 1/m) = Lateral strain /Longitudinal strain
8. Define principle stresses and principle plane.
Principle stress: The magnitude of normal stress, acting on a principal plane is
known as principal stresses.
Principle plane: The planes which have no shear stress are known as principal
Planes
9. What is the radius of Mohr’s circle?
Radius of Mohr’s circle is equal to the maximum shear stress.
10. What is the use of Mohr’s circle?
To find out the normal, resultant stresses and principle stress and their planes.
11. List the methods to find the stresses in oblique plane?
1. Analytical method
2. Graphical method.