πŸ“˜ Engineering Mechanics – Exam Written ...

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πŸ“˜ Engineering Mechanics – Exam Written Answers (2 Marks & 5 Marks)
(Diploma – Simple, Exam-Oriented Language)
⭐ Frequently Asked 2 Mark Questions
1. Define Force.
Answer:
Force is a push or pull acting on a body that changes or tends to change its state of rest or uniform motion, or changes its shape.
S.I Unit: Newton (N)
2. Define Moment.
Answer:
The turning effect of a force about a fixed point or axis is called the moment of a force.
Formula:
M=FΓ—d
Where:
F = Force
d = Perpendicular distance from the point to the line of action of the force.
S.I Unit: newton meter
3. Define Couple.
Answer:
A couple consists of two equal, opposite and parallel forces acting on a body at different points. A couple produces rotation only and no translational motion.
Moment of Couple:
M=FΓ—d
4. State Lami's Theorem.
Answer:
Lami's Theorem states that if a body is in equilibrium under the action of three coplanar concurrent forces, then each force is proportional to the sine of the angle between the other two forces.
sinΞ±
P
​
=
sinΞ²
Q
​
=
sinΞ³
R
​
5. Define Friction.
Answer:
Friction is the resisting force that opposes the relative motion or the tendency of motion between two surfaces in contact.
S.I Unit: Newton (N)
6. Define Centroid.
Answer:
The centroid is the geometrical centre of a plane figure where the entire area of the figure is assumed to be concentrated.
7. Define Centre of Gravity.
Answer:
The Centre of Gravity is the point through which the entire weight of a body acts vertically downward.
8. Define Mechanical Advantage (M.A.).
Answer:
Mechanical Advantage is the ratio of the load lifted by a machine to the effort applied.
M.A.=
Effort
Load
​
9. Define Velocity Ratio (V.R.).
Answer:
Velocity Ratio is the ratio of the distance moved by the effort to the distance moved by the load.
5 R
Distance moved by load
Distance moved by effort
​
10. Define Efficiency.
Answer:
Efficiency is the ratio of Mechanical Advantage to Velocity Ratio, expressed as a percentage.
Ξ·=
5 R
M.A.
​
Γ—100
11. Define Momentum.
Answer:
Momentum is the product of the mass of a body and its velocity.
p=mv
S.I Unit: kgΒ·meters per second
12. Define Work.
Answer:
Work is said to be done when a force causes a body to move through a certain distance in the direction of the force.
W=FΓ—s
S.I Unit: Joule (J)
13. Define Power.
Answer:
Power is the rate of doing work.
P=
t
W
​
S.I Unit: Watt (W)
14. Define Energy.
Answer:
Energy is the capacity of a body to do work.
S.I Unit: Joule (J)
15. Define Centripetal Force.
Answer:
Centripetal force is the force acting towards the centre of a circular path, which keeps a body moving in a circular motion.
F=
r
mv
2
​
⭐ Frequently Asked 5 Mark Questions
1. Parallelogram Law of Forces
Definition:
The Parallelogram Law of Forces states that if two forces acting simultaneously at a point are represented in magnitude and direction by the two adjacent sides of a parallelogram, then their resultant is represented by the diagonal of the parallelogram passing through the common point.
Steps to Draw:
Draw the two forces from the same point.
Complete the parallelogram.
Draw the diagonal from the common point.
The diagonal represents the resultant force.
Formula:
R=
P
2
+Q
2
2 P Q cosine theta
​
Applications:
Engineering structures
Crane design
Force analysis
2. Varignon's Theorem
Statement:
Varignon's Theorem states that the moment of the resultant of a system of forces about any point is equal to the algebraic sum of the moments of all the individual forces about the same point.
Mathematically:
M
R
​
=βˆ‘M
Applications:
Beam reaction calculations
Moment calculations
Structural analysis
3. Lami's Theorem
Statement:
If a body is in equilibrium under three coplanar concurrent forces, then each force is proportional to the sine of the angle between the other two forces.
sinΞ±
P
​
=
sinΞ²
Q
​
=
sinΞ³
R
​
Conditions:
Three forces only
Concurrent
Coplanar
Body in equilibrium
Applications:
Strings
Hooks
Crane joints
4. Free Body Diagram F.B.D
Definition:
A Free Body Diagram is a diagram showing a body isolated from its surroundings with all external forces and moments acting on it.
Steps to Draw:
Isolate the body.
Draw all applied forces.
Show weight, reactions and friction (if any).
Indicate directions of all forces.
Uses:
Solving equilibrium problems
Beam reactions
Friction analysis
5. Types of Friction
Definition:
Friction is the resisting force between two contacting surfaces.
Types:
Static Friction – Acts before motion starts.
Limiting Friction – Maximum static friction.
Sliding (Kinetic) Friction – Acts during sliding.
Rolling Friction – Acts when a body rolls.
Advantages:
Helps in walking.
Used in brakes and clutches.
Disadvantages:
Causes wear and tear.
Produces heat.
Reduces efficiency.
6. Angle of Friction & Angle of Repose
Angle of Friction
The angle between the resultant reaction and the normal reaction at limiting friction is called the angle of friction.
tanΟ•=ΞΌ
Angle of Repose
The angle of inclination of a plane with the horizontal at which a body just starts sliding is called the angle of repose.
tanΞΈ=ΞΌ
Relation:
Ο•=ΞΈ
​
7. Composite Centroid
Definition:
A composite section is formed by combining two or more simple plane figures.
Steps:
Divide into simple shapes.
Find the area of each shape.
Locate the centroid of each shape.
Calculate Ax and Ay.
Use:
x
Λ‰
=
βˆ‘A
βˆ‘Ax
​
y
Λ‰
​
=
βˆ‘A
βˆ‘Ay
​
8. Law of Machine
Statement:
The effort required to lift a load by a machine varies linearly with the load.
Equation:
P=mW+C
Where:
P = Effort
W = Load
m = Constant of the machine
C = Effort to overcome friction
Importance:
Predicts machine performance.
Helps determine machine efficiency.
9. Simple Screw Jack
Definition:
A screw jack is a lifting machine used to raise heavy loads by applying a small effort through a rotating handle.
Velocity Ratio:
5 R
p
2 pi R
​
Where:
R = Radius of the handle
p = Pitch of the screw
Applications:
Lifting cars
Workshops
Garages
10. Work, Power and Energy
Work
Work is done when a force moves a body through a distance.
W=Fs
Unit: Joule (J)
Power
Power is the rate of doing work.
P=
t
W
​
Unit: Watt (W)
Energy
Energy is the capacity to do work.
Types:
Kinetic Energy:
K.E
2
1
​
mv
2
Potential Energy:
P.E equals m g h
11. Equations of Motion
For uniform acceleration:
First Equation:
v=u+at
Second Equation:
s=ut+
2
1
​
at
2
Third Equation:
v
2
=u
2
+2as
Where:
u = Initial velocity
v = Final velocity
a = Acceleration
t = Time
s = Displacement
These equations are used to solve problems involving uniformly accelerated motion.
12. Newton's Second Law
Statement:
Newton's Second Law states that the rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction of the force.
Mathematical Expression:
F=ma
Where:
F = Force (N)
m = Mass (kg)
a = Acceleration (meters per second squared)
Applications:
Vehicle acceleration
Machine design
Motion analysis
Engineering calculations
⭐ Exam Tip
For 5-mark answers, always follow this order to score full marks:
Definition/Statement
Formula (if applicable)
Explanation
Diagram (whenever possible)
Applications/Uses (2 to 3 points)
This presentation is the one generally expected in diploma engineering examinations and helps maximize marks.
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