THANGA KASI RAJAN S ASSISTANT PROFESSOR, DEPARTMENT OF MECHANICAL ENGINEERING, KAMARAJ COLLEGE OF ENGINEERING AND TECHNOLOGY, VIRUDHUNAGAR

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ENGINEERING MECHANICS – GE6253
Important two mark questions
Unit I & II
1. Define Kinematics and Kinetics ?
Kinematics deals with the study of relationship between displacement, velocity, acceleration and
time of a given motion without considering the forces that causes motion.
Kinetics deals with the relationship between forces acting on the body, mass of the body and
motion of the body.
2. State Parallelogram law ?
If two vectors acting at a point be represented in magnitude and direction by the adjacent sides of a
parallelogram, then their resultant is represented in magnitude and direction by the diagonal of the
parallelogram passing through that point.
F2 R
F1
R = F1 + F2
3. State Triangle law?
If two vectors acting at a point are represented by the two sides of a triangle taken in order, then
their resultant is represented by the third side taken in opposite order
R F2
F1
R = F1 + F2
4. Define Lami’s Theorem?
If three forces acting at a point are in equilibrium, each force will be proportional to the sine of the
angle between the other two forces.
5. Define Principle of Transmissibility of force?
It states that “ The state of rest or of motion of a rigid body is unaltered if a force acting on the
body is replaced by another force of same magnitude and direction but acting anywhere on the body
provided the line of action remains same.
6. State Varignon’s Theorem?
“ The algebraic sum of moment of any number of forces about any point acting on a system is
equal to the moment of the resultant force about that point
7. Define moment of a force about a point?
It is defined as the product of a force and perpendicular distance of the line of action of the force
from a point.
8. Define a Couple?
Two equal parallel forces acting in opposite direction forms a couple
9. Define Resultant force?
It is a single force which replaces all other forces acting on the system is known as resultant force.
10. what is a force couple system?
The simple representation of a force and a couple in a system is known as force couple system.
Procedure for finding out: 1. find resultant force (Including its direction) and Net moment about the
given point. 2. Plot the resultant force at the given point along its direction and plot moment at the given
point.
11. What is a free body diagram?
It is the diagram of the body in which the body under consideration is free from all contact
surfaces and all the forces acting on it are clearly indicated.
P
Q
R
α
β
γ
= =

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12. State Equilibrium and its Conditions?
When resultant force acting on the system is Zere, then the system is said to be in equilibrium.
Conditions of Equilibrium are :
1. R=0 Fz=0 Mz=0
2. Fx=0 Mx=0
3. Fy=0 My=0
Forces:
Coplanar Force: - line of action of all forces acting on a system lie on same plane
Non Coplanar Force: - do not lie on same plane.
Coplanar collinear force: - line of action lie in same plane and same line
Coplanar concurrent force: - lie in same plane and act at one point
Coplanar non-concurrent force: - lie in same plane and act at different point.
Types of Equilibrium:
Stable Equilibrium : - If a body returns back to its original position after being slightly disturbed from
its rest position.
Unstable Equilibrium: - If a body does not returns back to its original position after being slightly
disturbed from its rest position.
Neutral Equilibrium: - If a body occupies a position and remains at rest in this position after being
slightly displaced from its rest position.
Unit III
1. Define Centroid or First moment of area?
It is defined as the point at which the total area of the plane figure namely rectangle, square etc.,
is assumed to be concentrated.
2. Define Center of Gravity?
The center of gravity of a body may be defined as the point through which the entire weight of the
body is assumed to be concentrated.
3. what is the difference between the center of gravity and centroid?
Center of gravity is applicable to solid bodies whereas centroid is applicable for only plane areas.
4. What is ‘ Surface of Revolution“ and “Body of Revolution” ?
Surface of Revolution: It may be defined as the surface which is generated by rotating a plane
curve namely Straight line, arc, etc., about a fixed axis in the plane of curve.
Body of Revolution: It may be defined as a body which is generated by rotating a plane area
namely triangular area, circular area etc., about a fixed axis.
5. Define Pappus-Guldinus Theorems?
Theorem 1: It states that the area of a surface of revolution is the product of the length of the
generating curve and the distance traveled by the centroid of the curve, while the surface is being
generated.
A = 2πyL (or) 2πxL
Theorem 2: It states that the volume of a body of revolution is obtained from the product of the
generating area and the distance traveled by the centroid of the area, while the body is being generated.
V = 2πyA (or) 2πxA
6. Define Moment of Inertia or Second moment of area?
Moment of Inertia of a body about any axis is the property by which the body resists rotation
about that axis.
In the case of plane figures Moment of Inertia is the second moment of the area of the plane figure
about the given axis.
Ixx=∫ y2
dA & Iyy = ∫ x2
dA
7. Define Radius of Gyration?
It is defined as the distance at which the entire area ‘A’ of the figure is assumed to be concentrated
such that the moment of Inertia about that axis is same.
I = area x (radius of gyration)2
8. State Parallel axis Theorem?
This theorem states that the moment of Inertia of a plane area about any axis is the sum of moment
of Inertia of the area about the axis passing through the centroidal axis and the product of the area of the
plane and square of the perpendicular distance of its centroid from the axis
Iaa = I + a h2
9. State Perpendicular Axis Theorem?
If Ixx and Iyy be the moment of Inertia about two mutually perpendicular axes x and y in the plane
and Izz be the moment of Inertia about the axis normal to the plane and passing through the point of
intersection of x and y axis then
Izz = Ixx + Iyy

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10. State Polar Moment of Inertia?
The area moment of Inertia for an area relative to an axis perpendicular to the plane of the area is
called polar moment of Inertia.
IP = Ixx + Iyy
11. Under what circumstances do the following coincide.
a) center of gravity and center of mass. b) center of gravity and centroid of area.
Center of gravity and center of mass coincides with the center of mass if gravitational forces are
taken to be uniform and parallel.
Centroid of area coincides with center of gravity of two dimensional bodies which are having
uniform thickness.
12. What is Principal axis and Principal Moment of Inertia?
If the Two Perpendicular Axes (x & y) is rotated then Ixy Values are changes accordingly. The
Perpendicular axes about which product moment of Inertia is zero are called Principal axes and the moment
of Inertia about these axes are called Principal moment of Inertia.
13. Define Mass moment of Inertia?
The property which measures the resistance of a body to angular acceleration is known as mass
moment of Inertia.
Unit IV
1. Define Kinematics?
Kinematics is the study of relationships between displacement, Velocity, acceleration and time of
a given motion , without considering the forces that cause the motion.
2. Define Kinetics?
Kinetics is the study of relationships between the forces acting on a body, the mass of the body
and the motion of the body.
3. What are the types of motion? Explain
Rectilinear motion: When the particle moves along the Straight line Path then the motion is said to be
Rectilinear
Curvilinear motion: When the particle moves along the curved path then that type of motion is said to
be curvilinear motion.
4. Define Average and Instantaneous Velocity?
Average Velocity: The average velocity of the particle over the time interval ∆t may be defined as the
quotient of the displacement ∆s and the time interval ∆t.
Instantaneous Velocity: Instantaneous velocity V of the particle at the instant t is obtained from the
average velocity by choosing shorter and shorter time intervals ∆t and displacement ∆s.
5. Define Average and Instantaneous acceleration?
Average acceleration: The average acceleration of the particle over the time interval ∆t may be defined as
the quotient of the velocity ∆t and the time interval ∆t.
Instantaneous acceleration: Instantaneous acceleration ‘a’ of the particle at the instant t is obtained from
the average acceleration by choosing shorter and shorter time intervals ∆t and velocity ∆v.
6. Define Motion Curve?
The curve obtained by plotting the Position, Velocity and acceleration against the time t is called
motion curve.
7. What you mean by uniform rectilinear motion and Uniformly accelerated rectilinear motion?
Uniform Rectilinear Motion: The motion of a particle in which the acceleration ‘a’ of the particle for
every value of ‘t’ is called uniform rectilinear motion.
Uniform accelerated Rectilinear Motion: The motion of the particle in which the acceleration ‘a’ of the
particle is constant is said to be uniformly accelerated rectilinear motion.
8.write down the equations of motion of a straight line?
V = u + at S = ut + ½ at2
V2
= u2
+ 2as
9. Define Relative motion and Dependent rectilinear relative motion?
Relative motion: when a motion of the body is evaluated with respect to another moving body, then the
motion is said to be relative motion.
Dependent rectilinear relative motion: When motion of one particle will depend upon the motion of
several other particles then that type of motion is said to be dependent Rectilinear relative motion.
10. What is projectile?
A particle/body projected upwards into space at an angle to the earth’s surface is called a
projectile. The shape of the path of the projectile is parabolic.
11. What is Trajectory?

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The path along which a projectile moves from the point of projection to the point where it meets
the ground is called the trajectory of the particle.
12. What is angle of Projection?
The angle at which a projectile is projected into space is called the angle of projection.
13. What is time of Flight?
Time during which the projectile is projected into space is called as Time of Flight.
14. What is the range of Projectile?
The velocity with which a projectile is projected into space is termed as the velocity of projection
15. State Newton’s Law ?
First Law: If the resultant force acting on a particle is zero then the particle remains at rest (if
originally at rest) or continue to move in straight line (if originally in motion)
Second Law: If the resultant force acting on a particle is not zero, then the acceleration of the
particle will be proportional to the resultant force acting in the same direction. Ie. F = ma
Third Law: To every action there is an equal and opposite reaction.
16. Define Linear Momentum and Angular Momentum?
Linear Momentum (L): The Vector mv (Product of Mass & Velocity) is called Linear
momentum of particle.
Angular Momentum (Ho) : Angular momentum Ho of a particle about a point ‘o’ is the moment
about ‘o’ of the Linear momentum (mv) of the particle at that instant. It is expressed in kg-m2
/s
Ho = r x mv(Cross Product)
17. Define Impulse?
If a constant force acts on a body for the given period of time , the product of force and time
during which it acts is termed as Impulse. The force which acts for this short interval is called impulsive
force.
18. Define Impact?
The phenomenon of collision of two bodies which occurs in a very small interval of time and
during which the two bodies exert very large force on each other is called an impact.
19. State Newton’s law of Collision of elastic bodies?
It States that “when two moving bodies collide with each other, their velocity of separation bears a
constant ratio to their velocity of approach”
Ie. Velocity of separation = (velocity of Approach) constant
v2 – v1 = e ( u1 – u2) where e – co-efficient of restitution
Co-efficient of Restitution: It is defined as the ratio of the relative velocity of their separation
after collision to the relative velocity of their approach before collision.
20. What is meant by plastic and elastic impact?
Elastic Impact: In this type of Impact there is no loss in energy. There fore the relative
velocities before and after impact are equal. (e = 1)
v2 – v1 = u1 – u2
Plastic Impact: In this case after collision, both the particles couple or stay together and move
with a common velocity (v) and the coefficient of restitution e = 0.
mA uA+ mB uB = (mA+ mB) v & vA = vB = v
21. Define Line of Impact?
The common normal area to the surfaces in contact during the impact is called the line of impact.
22. State law of conservation of Momentum?
The total momentum of two bodies remains constant before and after impact.
Initial momentum = Final momentum
mA uA+ mB uB = mAvA + mBvB
Unit V
Friction
1. What is meant by Friction?
When a body moves over another body, it experiences a opposing force at the contact surfaces.
This opposing force is called friction
2. State and explain the different types of friction?
Dry Friction: - Dry friction develops between the unlubricated surfaces of bodies in contact.
Fluid Friction: - Fluid friction developed between two surfaces in the presence of fluid when adjacent
layers of fluid are moving at different velocities.
Internal Friction: - Internal friction occurs in all solid materials which are subjected to cyclic loading.
3. State Coulomb’s law of dry friction

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Laws of Static Friction:
* The force of friction always acts in a direction, opposite to that in which the body tends to move
* The magnitude of the force of friction is always equal to the applied force.
Laws of Dynamic Friction:
 The force of friction always acts in a direction, opposite to that in which the body is moving
 For moderate speeds, the force of friction remains constant. But it decreases at a slow rate with
the increase in speed.
 The magnitude of dynamic friction is slightly less than that of static friction.
4. Define the following:
Static Friction:- If two surfaces, when are in contact, are at rest then the force experienced by one
surface is called as static friction
Dynamic Friction: If one surface starts moving and the other is at rest, then the force experienced
by the moving surface on the rest is called as dynamic friction.
Sliding Friction: - The friction experienced by a body when it slides over another body.
Rolling Friction: - The friction experienced by a body when it rolls over the other.
5. What is Limiting Friction
The maximum resistance offered by the body against the external Forces to move is known as
Limiting Friction(Fm).
6. What is impending motion?
The state of motion of a body which is just about to move or slide is called as impending motion.
The force required to cause this motion is called impending force.
7. Define angle of friction?
It is defined as the maximum angle (φ) between normal reaction and the resultant of the limiting friction
8. Define Angle of Repose?
The angle between an inclined plane and horizontal plane when a body placed on it, is just Start
moving down is called angle of repose.
9. What is wedge
A wedge is a piece of metal or wood in the shape of a prism to whose cross section is usually a
triangular or trapezoid. It is used for lifting heavy loads and tightening fits
10. Define Rolling Resistance?
It is defined as one of the friction occurs because of the deformation of the surface under a rolling load.
11. What is a belt drive?
A belt drive is a power transmission device with belt and pulley arrangement in which the belt
friction is used in application of brakes to stop motion.
12. Define Co-efficient of friction?
It is defined as the ratio of the limiting friction to the normal reaction between the two bodies and
is generally denoted by µ
Dynamics of Rigid body:
1. Define a rigid body?
It is defined as a body which does not deform the action of forces.
2. Define Translation, Rotation and General Plane Motion?
Translation: A rigid body is said to be in translation, if the linear displacement of every point in the
rigid body is the same.
Rotation: A rigid body is said to be in rotation, if all the particles of the body move along circles
centered on a fixed axis called axis of rotation.
General Plane Motion: A rigid body is said to be in General Plane Motion, if it undergoes a
combination of both translation and rotation.
3. Define Torque?
Torque is the turning moment of a force on the body in which it acts. Ie. T = Force x Radius
4. Define Instantaneous centre of Rotation of the plane motion?
In general plane motion of a rigid body at any given instant the velocities of various particles of
the slab are same as if the slab bear rotating about certain axis perpendicular to the plane of the slab called
the instantaneous centre of rotation of the slab.
The instantaneous centre point is identified with the body where the velocity is zero.
5. Define Inertia Force?
Inertia Force of a body can be defined as the resistance to the change in the condition of rest or of
uniform motion of body
The magnitude of the inertia force is the product of mass and acceleration of the particle and its
direction is opposite to the direction of acceleration of the particle.
6. State D’Alembert’s principle?

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ΣF – ma =0 where –ma is called inertia force
The force system consisting of external forces and inertia force can be considered to keep the
particle in equilibrium since the resultant force externally acting on the particle is not zero. The particle is
said to be in dynamic equilibrium.