EMECH 2 Marks
EMECH 2 Marks
EMECH 2 Marks
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.
16. Two vectors are equal if
Ans: Their magnitudes, direction and the sense are the same and lie anywhere in space)
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.
37. What is stable equilibrium?
A body is said to be in stable equilibrium, if it returns back to its original position after it
is slightly displaced from its position of rest.
38. What is unstable equilibrium?
A body is said to be in unstable equilibrium, if it does not return back to its original
position and heels farther away after slightly displaced from its position of rest.
39. 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..
40. 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
Equilibrium of Rigid bodies
1. The position vector and force are 2i - 3j + 4k and 120i - 260j + 320k respectively. Find
the moment of the Force about the origin. And also find the scalar quantity of the
moment.
Mo= r X F
= 80i-160j-160k
Scalar quantity =
= =240units
2. In the above problem, find the angles made by the moment along x, y and z axes
=0.324i+0.489j+0.811k
o N
F
r
MON = ON· Mo
Mo = r X F
12. State the requirements for equilibrium of a body acted upon by a parallel
force system?
1. The algebraic sum of the forces is zero.i.e., .F=0.
2. The algebraic sum of the moments about any point is zero. i.e., .M=0.
13. Draw the free body diagram of a ball (sphere) of weight W, resting on a frictionless
plane surface shown below.
RA
14. Draw the free body diagram of a ladder of weight W, leaning against a smooth wall,
shown below.
NA RB
B
W
A FA
15. A block of weight W, kept on a levelled rough surface is acted upon by a tensile force
F. Draw the free body diagram. W
A F F
FA NA
16. If the above block rests on an inclined rough surface, draw the free bodies diagram
A W
N A FA
17. Refer the figure shown below and draw the free body diagram
R1
RC
RC
WA R2
WB
18. Refer the figure shown below and draw the free body diagram
C
A
A2 C3 A R3 R6
AR 3
1 6 R2 R3
B R1 R2 WC
4 5 WA B
R2 R5
WB
19. What are the necessary and sufficient conditions for the equilibrium of a rigid body in
three dimensions?
FX= 0 MX = 0
FY= 0 MY =0
FZ= 0 MZ =0
20. What are the common types of supports used in two dimensions?
1. Roller support
2. Hinged support
3. Fixed support
21. What are the common types of supports used in three dimensions?
1. Ball support
2. Ball and Socket support
3. Fixed (or Welded) support
22. Define equilibrant?
The force which brings the system of forces into equilibrium is called equilibrant. It is
equal to the resultant force in magnitude collinear but opposite in nature.
23. What are the common types of loads?
1. Point load (or concentrated load)
2. Uniformly distributed load
3. Uniformly varying load
24. What is statically determinate structure?
A structure which can be completely analysed by static conditions of equilibrium (.H
=0; V =0 and M=0) alone is statically' determinate structure.
UNIT -III
Properties of Surfaces and Solids
1. Define Centre of Gravity.
Centre of Gravity is an imaginary point at which the entire weight of the body is
assumed to act.
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
9. The centre of gravity of an equilateral triangle with each side measuring 'a' is from
any of the three sides. (Ans: )
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
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
23. The Radius of gyration of the mass of a body with respect to x-x axis isk =
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)
30. Second moment of area with respect to a set of perpendicular axes is known 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 known as------------
(Ans: Principal moment of Inertia)
33. Mass M.I of thin plate about any axis------- (Ans: volume x Density x Area M.I of the
plate about the same axis)
UNIT-IV
Dynamics of Particles
1. Define 'speed
The rate of change of displacement of a body irrespective of its direction is
called speed. It‟s a scalar quantity
2. Define velocity
The rate of change of displacement of a body with respect to its surroundings in a
particular direction is called the velocity. It is a vector Quantity.
3. Define acceleration
The rate of change of velocity of a body is called acceleration.
9. Distance travelled by a body in the nth second of its motion is --------- (u+a/2(2n-1))
The sum of the moments about '0' of the forces acting on the particle is equal to twice
the rate of change of angular momentum of the particle about „0‟)
P V1
P
Let a particle has a velocity V at time t and a velocity V' (= V + I:l V) at P and P'
respectively as shown in fig (a). To study the time rate of change, the two velocity vectors are
plotted such that their tails are located at the fixed point '0' and their arrow heads touch points
on the dashed curve as shown in fig (b) This curve is called as Hodograph.
P.S =W/2g(v2-u2)
P- Force, S-distance travelled
W- Weight of the body, g- acceleration due to gravity
v- Final velocity, u- initial velocity
1. Define friction
Friction may be defined as a force of resistance acting on a body which prevents or
retards slipping of the body relative to a second body or surface with which It is in contact
c) Limiting friction bears a constant ratio to the normal reaction between the two
surfaces
d) The force of friction is independent of the area of contact between the two surfaces
e) The force of friction depends upon the roughness of the surfaces.
c) Limiting friction bears a constant ratio to the normal reaction between the two
surfaces
d) The force of friction is independent of the area of contact between the two surfaces
e) The force of friction depends upon the roughness of the surfaces.
17. once a body just begins to slide, it continues to slide, because --------------------------
(Ans: The frictional force becomes less)
19. The ratio between the tensions in the tight side and slack side of
a flat belt drive increases --------------------
(Ans: Exponentially as the angle of lap increases)