What is mechanism?
A mechanism is an assembly of different parts which perform a complete motion and
is often part of a machine.
State Newton's three laws of Motion.
- The law of inertia: Every object in a state of uniform motion tends to remain
in that state of motion unless an external force is applied to it.
- Acceleration is produced when a force acts on a mass. The greater the mass (of
the object being accelerated) the greater the amount of force needed (to
accelerate the object). Force=Mass times acceleration.
- For every action there is an equal and opposite reaction.
State the laws of thermodynamics and its importance of in Mechanical Engineering.
Thermodynamics is a physical science which studies the interrelation between
heat, work and the internal energy of any system. Thermodynamics helps study all
the systems of mechanical engineering. There are three laws of thermodynamics.
First Law: Energy can be neither created nor destroyed. It can only change forms.
In any process in an isolated system, the total energy remains the same.
Eg: turning on a light would seem to produce energy; however, it is electrical
energy that is converted.
Second Law: The second law of thermodynamics states that the entropy of any
isolated system not in thermal equilibrium almost always increases.
Eg: A car that has run out of gas will not run again until you walk 10 miles to a
gas station and refuel the car.
Third Law: As temperature approaches absolute zero, the entropy of a system
approaches a minimum.
Eg: Water in gas form has molecules that can move around very freely. Water vapor
has very high entropy (randomness). As the gas cools, it becomes liquid which
can still move around but not as freely. At this point they have lost some
entropy. On cooling further it becomes solid ice where molecules can no longer
move freely but can only vibrate within the ice crystals. The entropy is now
very low. As the water nears absolute zero, the vibration of the molecules
diminishes. If the solid water reaches absolute zero, all molecular motion would
stop completely. And at this point the water would have no entropy at all.
What is Hess law?
According to the Hess law the energy transfer is simply independent of the way
being followed. If the reactant and the product of the whole process are the
same then same amount of energy will be dissipated or absorbed.
What is PS?
Personal Statement. It is something that gives an informative background about an
What is a bearing? What are the different types of bearings?
Bearing is a device that helps smoother movement with minimal friction which in
turn helps enhances efficiency and speed. Considering two types of loading,
radial and thrust, there are different types of bearings which help handle these
loads. The basic difference in the types of loads is essentially due to their
ability to handle weight and different kinds of loads for various applications.
Different types of bearings are:
-Ball Thrust bearing
-Roller thrust bearing
-Tapered roller bearing
-Giant Roller Bearing
What is a process flow diagram?
A Process Flow Diagram is a user friendly, simplified sketch which illustrates
general plant streams, major equipments and key central loops and shows the
relationship between major components in the system. By using symbols to
identify instruments and vessels it describes the primary flow course. They also
provide e detail of mass/energy balance data along with stream composition and
physical properties, however do not show minor components.
What is a time and motion theory?
Frederick Taylor was pioneer of the time and motion theory. This technique
monitors the amount of time required to complete a task along with observing the
steps taken by a worker to complete the given task.
Which is the hardest material on earth?
Diamond is currently the hardest material, made up of carbon atoms which cannot
move. Carbon is the only atom that can have four electrons in the second shell
surrounding the carbon nucleus, precisely why making a diamond the hardest
material. However, there also are claims by a few to a new rare material called
Wurtzite Boron Nitride which has a structure similar to a diamond but has some
other atoms in place of carbon.
One unit of BTU is how many Joules?
1 BTU=1055.06 Joules
What does a pump develop? Give reason to support your answer.
Pump is a device that is used to transfer fluid from one place to another place
which means it develops flow not pressure.
Explain the difference between pipe and a tube.
A pipe is measured based on its inner diameter (ID) whereas a tube is measured
based on the outer diameter (OD). Other than the dimensions there is no major
difference between the two.
Explain the formula of heat loss in a pipe.
In order to find total heat loss through the pipes it is imperative to know the
thermal conductivity and the differing thicknesses of each layer. The ground
that surrounds the pipe also acts as a layer of insulation. Considering this,
the thermal properties of the stoneless sand is included in the heat loss
What kind of pipes are used for steam lines?
Pressure and temperature are two of the most important factors to be considered
before selecting the type of material to be used. Steam is a compressible gas
due to which the capacity of the pipe line depends on the size of the pipes and
pressure of the steam. Since steam at even low pressure can be dangerous, extra
care is to be taken. Galvanized pipes are usually not used for steam. Pipes made
of mild steel with welded fittings are instead largely used.
Who invented the four stroke engine? According to you which one is more
efficient, four stroke engine or a two stroke engine and why?
Nikolaus Otto invented the four stroke engine. Both, two stroke and four stroke
have their own advantages and disadvantages. 4 stroke is more fuel efficient.
However, 2 stroke produces more power.
What do you understand by the concept of a 6 stroke engine? Explain how it works.
The six stroke engine is based on the concept of four stroke engine but built
with an intention of improvising the efficiency in reducing emission. Every
cycle of a four stroke engine involves the upward and downward movement of the
piston which happens twice in the chamber, resulting in four total strokes and
one of which is the power stroke which provides the torque to move the vehicle.
A six stroke engine works similarly except that there are two power strokes.
Explain what is torque
Torque is the force that causes rotation. It is a measure of how much force is
acting on an object making it rotate.
What is the difference between torque and power?
While power determines the speed of a vehicle, torque determines the time in
which that speed can be reached. The greater the torque figure, the faster the
acceleration. The more torque in the engine, the faster you accelerate. Power is
the rate at which work is done, so it is basically the potential of the engine.
Explain why diesel engine is known as high torque and petrol engine as high speed
Each power stroke in a petrol engine releases more heat and is converted into
mechanical energy due to a higher rate of burning. This is the reason petrol
engine has higher power and acceleration.
Diesel engine is a compression ignition engine with higher compression ratio,
therefore extreme pressure is high. Since the piston of a diesel engine is
larger, more torque is delivered in produced.
Why do heavy vehicles use diesel engine?
The compression ratio of diesel engine is higher than the petrol engine, the
reason for producing higher torque. The efficiency of diesel engine increases
with load. Diesel produces slow energy on burning of fuel and the efficiency of
the engine increases with load which is why diesel engine is suitable and
largely used for heavy vehicles.
Explain the difference between projectile motion and rocket motion.
The major difference is that a projectile has no motor or a rocket on it, due to
which the momentum is given to it as it is launched. A pen thrown across a room
is a classic example of a projectile motion. On the other hand, a rocket or
missile has a motor on it which helps in accelerating while moving. This helps
in resisting other forces such as gravity. A projectile does not have any
specific shape, it is a point mass, whereas rocket has a particular shape having
its center of gravity situated at a particular point on its body. Thus rocket
motion comes under kinetics and projectile comes under kinematics.
Between steel, copper and brass, which conduct faster heat.
Copper conducts heat faster than steel or brass. In most cases, material that is
good for conducting heat is also good for electricity.
Explain the types of sensors.
(i) Temperature Sensor- This device collects information about the temperature
from a source and converts it to a form which is understandable by another
device or person. Glass thermometer is the best example where mercury acts as
the temperature sensor.
(ii) IR Sensors- This device detects and/or emits infrared radiation to sense a
particular phase in the environment. Mostly thermal radiation is emitted by all
the objects in the infrared spectrum. This type of radiation is not visible to
the human eye but the infrared sensor detects it.
(iii) UV Sensors- These sensors measure the intensity of the ultraviolet
radiation. This form of electromagnetic radiation has wavelengths which are
longer than x-rays yet shorter than visible radiation. UV sensors can discover
the exposure of environment to ultraviolet radiation.
(iV) Touch Sensor- A touch sensor acts as a variable resistor based on the
location where it is sensed. Proximity Sensor- A proximity sensor detects the
presence of objects that are placed in close proximity without any point of
What minerals are used in the manufacture of cars?
Cars are made from many various minerals. The steel body is made from the
iron-rich minerals like magnetite and hematite. Door handles and badges are
often coated in chromium which comes from chromite. Some of the other minerals
used are aluminum, quartz, copper, magnesium, zinc, tin etc.
Which instrument measures speed in a car?
A speedometer helps measure the speed in the car.
What are the advantage and disadvantage of using LPG in a car?
The high octane rate enables it to blend better with air and to burn completely,
generating less carbon. With less carbon buildup, spark plugs often last longer
and oil changes are needed less frequently.
Since it burns in the gaseous phase, it results in less corrosion and engine
In case of a spill, LPG evaporates quickly.
The LPG requires servicing at approximately once a year.
Since complete combustion occurs, more heat is liberated which is not advised for
a long journey as the engine will get over heated.
Installation of LPG is rather difficult.
Why gas containers are mostly in a cylindrical shape?
The ideal shape would be a sphere. The container must have the capacity to
withstand the extremely high pressure of liquefied gas. A spherical shape helps
in distributing these forces uniformly.
Explain why re-heater is used in gas turbine
The advantage of reheater is that it significantly increases the thrust; which is
a prime reason for its use in gas turbines.
How many types of suspensions are used in automobiles?
What is DTSI? Why it is used in motor bikes?
Digital Twin Spark Ignition. This is used for a better fuel combustion in the
cylinder head which helps provide better efficiency and optimum use of fuel.
What are the advantages of DTSI over normal engines?
The cylinder head has two spark plugs, instead of the usual one. When two sparks
are generated at either ends of the combustion chamber, the air-fuel mixture is
ignited in a way that creates two flame fronts. A higher rate of combustion is
achieved leading to higher rise in pressure. The outcome of this is more torque,
better fuel efficiency and lower emissions.
What is meant by gear ratio?
A gear ratio is a direct measure of ratio of the rotational speeds of two or more
What is the ratio of specific heat of air?
The ratio of specific heat γ=CP/CV is a factor in adiabatic engine processes and
in determining the speed of sound in gas. This ratio γ=1.66 for an ideal
monoatomic gas and γ=1.4 for air, which is predominantly a diatomic gas.
What is the percentage of carbon present in pig iron?
Carbon content is generally 3.5-4.5%.