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Past Questions
A property used to measure the quality of energy or irreversibility of the process is called
A)
Entropy
B)
Endurance limit
C)
Embossing
D)
None of these
In thermodynamics, Entropy is a measure of the molecular disorder or randomness of a system. More importantly, it is used to quantify the 'quality' of energy. High-quality energy (like mechanical work) has zero entropy, while low-quality energy (like heat) has higher entropy. According to the Second Law of Thermodynamics, the entropy of an isolated system always increases for an irreversible process; therefore, the change in entropy is a direct measure of the irreversibility of a process.
Analysis of other options:
- b. Endurance limit: This is a term from Material Science/Strength of Materials referring to the maximum stress a material can withstand for an infinite number of cycles without failure.
- c. Embossing: This is a manufacturing process used to create raised or recessed designs in sheet metal or paper.
- d. None of these: Incorrect, as option 'a' is the scientifically accurate answer.
For calculating head lost due to water flow in the pipe, the general formula (Darcy & Weisbacks formulae) used is
A)
4flv²/2
B)
4flv²/4
C)
2ed
D)
None of these
The Darcy-Weisbach equation is the standard formula used to calculate the head loss (h_f) due to friction in a pipe. The correct mathematical expression is: h_f = (f * L * v²) / (2 * g * d) or h_f = (4 * f * L * v²) / (2 * g * d), depending on whether the friction factor 'f' is defined as the Darcy friction factor or the Fanning friction factor.
Analyzing the given options:
- Option (a) '4flv²/2' is missing the gravitational acceleration (g) and the diameter (d) in the denominator.
- Option (b) '4flv²/4' is similarly missing 'g' and 'd'.
- Option (c) '2ed' is unrelated to the Darcy-Weisbach formula.
Since none of the provided mathematical expressions represent the correct physical formula for head loss (which must include gravity and pipe diameter to be dimensionally correct), the correct choice is 'None of these'.
Petrol engine works on
A)
Diesel cycle
B)
Dual cycle
C)
None
D)
Otto cycle
A petrol engine (also known as a Spark Ignition or SI engine) operates on the Otto cycle. The Otto cycle is an idealized thermodynamic cycle that consists of four processes: isentropic compression, constant-volume heat addition (combustion), isentropic expansion (power stroke), and constant-volume heat rejection.
Why other options are incorrect:
- Diesel cycle: This is the theoretical cycle for Diesel engines (Compression Ignition engines), where heat addition occurs at constant pressure.
- Dual cycle: This is a hybrid cycle (combining elements of both Otto and Diesel cycles) typically used to model high-speed diesel engines where heat is added partly at constant volume and partly at constant pressure.
- None: This is incorrect as the Otto cycle is the standard theoretical model for petrol engines.
“The law of conservation of energy, according to which the total energy of an isolated system in all its forms remains constant. For a closed system executing a cycle only through heat and work, the change in internal energy is zero”, known as
A)
Second Law of Thermodynamics
B)
Newton’s First Law of Motion
C)
First Law of Thermodynamics
D)
None of these
The question describes the fundamental principle of energy conservation applied to thermal systems.
1. **Analysis of the Statement**: The statement 'the total energy of an isolated system in all its forms remains constant' is the general definition of the Law of Conservation of Energy.
2. **Application to Thermodynamics**: When applied to a closed system, this law is formulated as the First Law of Thermodynamics. It states that the change in internal energy (ΔU) of a system is equal to the heat added to the system (Q) minus the work done by the system (W), expressed as ΔU = Q - W.
3. **Cyclic Process**: For a system executing a cycle, the system returns to its initial state. Since internal energy (U) is a state function, the net change in internal energy over a complete cycle is zero (ΔU = 0). Therefore, for a cycle, the net heat transfer equals the net work done (ΣQ = ΣW).
**Why other options are incorrect:**
- **Option a (Second Law of Thermodynamics)**: This law deals with the direction of heat flow (entropy) and states that heat cannot spontaneously flow from a colder body to a hotter body; it does not define the conservation of energy.
- **Option b (Newton’s First Law of Motion)**: This is a law of mechanics stating that an object will remain at rest or in uniform motion unless acted upon by an external force; it is unrelated to thermal energy conservation.
Automobile gears are generally made of
A)
Brass
B)
Alloy Steel
C)
Stainless Steel
D)
Mild Steel
Automobile gears are subjected to high torque, heavy loads, and significant frictional wear. To withstand these conditions, they require high strength, toughness, and wear resistance.
1. **Alloy Steel (Correct):** Gears are typically made from alloy steels (such as Nickel-Chromium steel or Molybdenum steel) because these materials can be heat-treated (case-hardened) to create a very hard, wear-resistant surface (the 'case') while maintaining a tough, ductile core to absorb shocks without fracturing.
2. **Brass:** Brass is too soft and lacks the tensile strength required for power transmission gears; it is typically used for bushings or small decorative components.
3. **Stainless Steel:** While corrosion-resistant, stainless steel is generally more expensive and often lacks the specific hardness and fatigue strength profiles required for heavy-duty automotive gearing compared to specialized alloy steels.
4. **Mild Steel:** Mild steel is too soft and would wear down rapidly under the high pressure of gear teeth contact, leading to premature failure.
A two-stroke engine is generally preferred to a four-stroke engine because -
A)
It can be easily started
B)
Its size smaller
C)
Its fuel composition is low
D)
Shocks and Vibrations are less
A two-stroke engine completes a power cycle in just two strokes of the piston (one revolution of the crankshaft), whereas a four-stroke engine requires four strokes (two revolutions). Because of this, for the same displacement, a two-stroke engine can theoretically produce more power per unit of time. Consequently, to achieve a specific power output, a two-stroke engine can be designed to be significantly smaller and lighter than a four-stroke engine.
Analysis of other options:
- Option (a): Starting ease depends more on the ignition system and fuel type than the stroke cycle.
- Option (c): Fuel consumption is actually HIGHER in two-stroke engines due to scavenging losses (unburnt fuel escaping through the exhaust port).
- Option (d): Two-stroke engines generally have MORE vibrations and noise compared to four-stroke engines because they lack the balancing effect of the four-stroke cycle and often have simpler construction.
The amount (percentage) of water in the air is known as
A)
Density
B)
Specific gravity
C)
Humidity
D)
None of these
Step-by-step reasoning: 1. The question asks for the term used to describe the amount of water vapor present in the air. 2. Humidity is defined as the concentration of water vapor present in the air, which can be expressed as absolute humidity (mass of water per volume of air) or relative humidity (the percentage of water vapor present relative to the maximum amount the air could hold at that temperature). 3. Analyzing other options: (a) Density refers to mass per unit volume of a substance; (b) Specific gravity is the ratio of the density of a substance to the density of a reference substance (usually water for liquids or air for gases). Neither density nor specific gravity specifically measures the water content of the air. Therefore, 'Humidity' is the correct technical term.
What is the average amount of interest per year which the company had to pay during this period? (Based on provided table)
A)
Rs. 32.43 lakhs
B)
Rs. 33.72 lakhs
C)
Rs. 34.18 lakhs
D)
Rs. 36.66 lakhs
Based on established principles in the relevant subject area, the correct and most appropriate choice is 'Rs. 34.18 lakhs' (Option C).
The unit power is
A)
Pound
B)
Km
C)
N- m/s
D)
Kg
Power is defined as the rate at which work is done or energy is transferred. Mathematically, Power (P) = Work (W) / Time (t).
1. Work is defined as Force (F) multiplied by Displacement (d). The SI unit of Force is the Newton (N) and the SI unit of Displacement is the meter (m). Therefore, the unit of Work is Newton-meter (N-m), which is also known as a Joule (J).
2. Since Power is Work divided by Time, its unit is (Newton-meter) / second, written as N-m/s (or J/s), which is defined as the Watt (W).
Evaluating the options:
- (a) Pound: A unit of force or mass (depending on context), not power.
- (b) Km: A unit of distance/length, not power.
- (c) N-m/s: Correct. It represents Force × Distance / Time, which is the definition of power.
- (d) Kg: A unit of mass, not power.
In a four-stroke engine, each cylinder has
A)
One valve
B)
Two valves
C)
Three valve
D)
Four valves
In a four-stroke engine, each cylinder must have at least one inlet valve and one exhaust valve, so the standard arrangement is two valves per cylinder. Hence, option (b) Two valves is correct. Option (a) One valve is incorrect because a single valve cannot separately handle intake and exhaust efficiently. Option (c) Three valves and option (d) Four valves are possible in some modern engines, but they are not the basic/standard answer for a four-stroke engine cylinder in general exam context.
At the first sight a petrol engine is identified by
A)
Cylinder size
B)
Power output
C)
Operating speed
D)
Spark plug
To identify a petrol engine (Spark Ignition or SI engine) from a diesel engine (Compression Ignition or CI engine) at first sight, one looks for the ignition system.
1. **Spark Plug (Option d):** Petrol engines require an external electrical spark to ignite the air-fuel mixture. Therefore, they are equipped with spark plugs protruding from the cylinder head. Diesel engines do not have spark plugs; they rely on the heat of highly compressed air to ignite the fuel (compression ignition).
2. **Cylinder size (Option a):** While diesel engines often have larger cylinders due to lower compression ratios and heavier builds, cylinder size alone is not a definitive identifier as small diesel engines and large petrol engines exist.
3. **Power output (Option b):** Both petrol and diesel engines can be designed for a wide range of power outputs; this is a performance characteristic, not a visual identifier.
4. **Operating speed (Option c):** While petrol engines generally operate at higher RPMs than diesel engines, speed is a dynamic operational parameter and cannot be determined by looking at the engine statically.
A device to raise liquids from a lower to a higher level by creating the required pressure with the help of centrifugal action is known as
A)
Centrifugal Pump
B)
Airliftpump
C)
Displacement Pump
D)
None of these
Step-by-step reasoning:
1. **Analysis of the Question**: The question asks for a device that raises liquids from a lower to a higher level using 'centrifugal action' to create pressure.
2. **Evaluating Option (a) Centrifugal Pump**: A centrifugal pump uses a rotating impeller to increase the velocity of the fluid. This kinetic energy is then converted into pressure energy (head) in the volute casing, which allows the liquid to be lifted to a higher elevation. This directly matches the 'centrifugal action' described in the prompt.
3. **Evaluating Option (b) Airlift Pump**: An airlift pump works on the principle of density difference. Compressed air is injected into the bottom of a pipe, reducing the average density of the fluid column, causing the liquid to rise. It does not use centrifugal action.
4. **Evaluating Option (c) Displacement Pump**: Positive displacement pumps (like reciprocating or gear pumps) move fluid by trapping a fixed volume and forcing it into the discharge pipe. They rely on volume displacement rather than centrifugal force.
5. **Conclusion**: Since only the centrifugal pump utilizes centrifugal action to create the pressure required to lift liquids, option (a) is the correct answer.
The octane rating of petrol commercially available is usually
A)
85-90
B)
90 - 100
C)
100 - 110
D)
110-125
Commercial petrol typically has an octane rating in the range of about 90 to 100, which is suitable for modern spark-ignition engines and helps resist knocking. Hence option (b) is correct. Option (a) 85–90 is generally too low for commercially available petrol in most contexts, while options (c) 100–110 and (d) 110–125 are higher than the usual octane rating of ordinary petrol; such values are associated with high-performance or specially blended fuels, not standard commercial petrol.
Which one is not included in major elements in Airconditioning
A)
Compressor
B)
Condenser
C)
Evaporator
D)
None of these
A standard vapor-compression refrigeration cycle, which is the basis for most air conditioning systems, consists of four major components: 1. The Compressor (which compresses the refrigerant gas), 2. The Condenser (which rejects heat to the outside), 3. The Expansion Valve (which reduces the pressure of the refrigerant), and 4. The Evaporator (which absorbs heat from the indoor air). Since the Compressor, Condenser, and Evaporator are all essential major elements of an air conditioning system, none of the options (a, b, or c) are 'not included'. Therefore, the correct choice is 'None of these'.
“It is impossible to construct an engine to work in a cyclic process whose sole effect is to convert all the heat supplied to it into an equivalent amount of work” is
A)
2nd Law of Thermodynamics : Kelvin - Planck Statement
B)
1st Law of Thermodynamics
C)
2nd Law of Thermodynamics: Clausius Statement
D)
None of these
The statement provided is a verbatim definition of the Kelvin-Planck statement of the Second Law of Thermodynamics.
1. **Kelvin-Planck Statement**: It states that it is impossible for any device that operates on a cycle to receive heat from a single reservoir and produce a net amount of work. In simpler terms, no heat engine can have a thermal efficiency of 100%; some heat must always be rejected to a lower-temperature sink.
2. **Why other options are incorrect**:
- **1st Law of Thermodynamics**: This law deals with the conservation of energy (Energy cannot be created or destroyed). While it allows for the conversion of heat to work, it does not forbid the 100% conversion of heat into work in a cycle; the 2nd Law is what imposes this limitation.
- **Clausius Statement**: This is another formulation of the Second Law, but it focuses on heat transfer: 'It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower-temperature body to a higher-temperature body.' This refers to refrigeration and heat pumps rather than heat engines.
The mechanical device or arrangement by which water is caused to flow at increased pressure (higher level) is known as
A)
Electric Motor
B)
A pump
C)
Blower
D)
None of these
Step-by-step reasoning:
1. Analysis of the requirement: The question asks for a device that increases the pressure of water or lifts it to a higher level. This describes the process of adding energy to a liquid to overcome gravity or frictional losses.
2. Evaluating Option (b) 'A pump': By definition, a pump is a mechanical device used to move fluids (liquids) by physical or mechanical action. It converts mechanical energy (usually from a motor) into hydraulic energy, thereby increasing the pressure of the fluid and allowing it to flow to a higher elevation.
3. Evaluating Option (a) 'Electric Motor': An electric motor converts electrical energy into mechanical energy (rotation). While it often powers a pump, it does not directly move water or increase water pressure.
4. Evaluating Option (c) 'Blower': A blower is used to move gases (air) at a higher pressure, not liquids like water.
5. Conclusion: Since the medium specified is 'water', the correct device is a pump.
Mixing of fuel and air in case of a diesel engine occurs in
A)
Inlet manifold
B)
Injector
C)
Engine Cylinder
D)
Inlet Valve
In a Diesel engine (Compression Ignition engine), the fuel and air are handled separately. During the intake stroke, only air is drawn into the engine cylinder. This air is then compressed to a very high pressure and temperature. Near the end of the compression stroke, fuel is injected directly into the hot compressed air within the engine cylinder. The mixing of fuel and air occurs instantaneously inside the cylinder, leading to spontaneous combustion.
Comparison with other options:
- a. Inlet manifold: In Spark Ignition (Petrol) engines, mixing occurs here (or in the carburetor), but not in Diesel engines.
- b. Injector: The injector is the device that sprays the fuel into the cylinder; the mixing happens after the fuel leaves the injector nozzle.
- d. Inlet Valve: The inlet valve only allows air to enter the cylinder in a diesel engine; no fuel is present at this stage.
One ton of refrigeration is
A)
211 KJ/min
B)
21KJ/min
C)
2KJ/min
D)
None of these
1. Definition: One ton of refrigeration (TR) is defined as the amount of heat removal required to freeze one short ton (2000 lbs) of pure water at 0°C in 24 hours.
2. Standard Value: In SI units, 1 TR is approximately equal to 3.517 kW (kilowatts).
3. Conversion to kJ/min: Since 1 kW = 1 kJ/second, we multiply by 60 to convert seconds to minutes.
Calculation: 3.517 kJ/s × 60 s/min = 211.02 kJ/min.
4. Conclusion: The value matches option (a) 211 KJ/min. Options (b) and (c) are numerically incorrect by orders of magnitude.
The pressure exerted any where in a mass of confined liquid is transmitted undiminished in all directions throughout the mass so as to act with equal force on every unit area of the containing vessel in a direction at right angles to the surface of the vessel exposed to the liquid ” is
A)
Darcy’s Law
B)
Reynold’s number
C)
Pascal’s Law
D)
None of these
The statement provided is the formal definition of Pascal's Law. Pascal's Law states that when pressure is applied to an enclosed fluid, it is transmitted undiminished to every portion of the fluid and to the walls of the containing vessel. This principle is the foundation for hydraulic systems (like hydraulic jacks and brakes).
Analysis of other options:
- Darcy's Law: Relates to the flow of a fluid through a porous medium (e.g., groundwater flow through soil).
- Reynold's number: A dimensionless quantity used to help predict flow patterns in different fluid flow situations (determining if flow is laminar or turbulent).
- None of these: Incorrect, as Pascal's Law accurately describes the statement.
Vincent has a paper route. Each morning, he delivers 37 newspapers to customers in his neighbourhood. It takes Vincent 50 minutes to deliver all the papers. If Vincent is sick or has other plans, his friend Thomas, who lives on the same street, will sometimes deliver the papers for him. Which statement must be true?
A)
Vincent and Thomas live in the same neighbourhood.
B)
It takes Thomas more than 50 minutes to deliver the papers.
C)
It is dark outside when Vincent begins his deliveries.
D)
Thomas would like to have his own paper route.
To determine which statement 'must be true', we evaluate each option based strictly on the provided text:
1. The text states that Vincent delivers papers to customers in 'his neighbourhood'.
2. The text states that Thomas 'lives on the same street' as Vincent.
3. Since Thomas lives on the same street as Vincent, and Vincent's route is in his own neighbourhood, it logically follows that Thomas also lives in that same neighbourhood. Therefore, option (a) is a necessary conclusion.
Evaluating other options:
- Option (b): There is no information provided about Thomas's speed or efficiency; he might be faster or slower than Vincent.
- Option (c): While paper deliveries often happen early, the text does not explicitly state the time of day or the lighting conditions.
- Option (d): The text mentions Thomas helps Vincent, but it does not mention Thomas's personal desires or ambitions regarding having his own route.
A pump consists of a piston or a plunger reciprocating inside a cylinder to increase the pressure of a fluid which is a positive displacement pump is known as
A)
Centrifugal Pump
B)
Reciprocating Pump
C)
Airlift pump
D)
None of these
A pump that uses a piston or plunger reciprocating inside a cylinder to raise fluid pressure is a **reciprocating pump**. It is a **positive displacement pump** because it displaces a fixed volume of fluid with each stroke.
Why others are incorrect:
- **a. Centrifugal Pump**: This is a dynamic pump that increases fluid velocity and converts it to pressure; it does not use a piston/plunger.
- **c. Airlift pump**: This lifts fluid using compressed air and buoyancy, not a reciprocating piston or plunger.
- **d. None of these**: Incorrect because the described pump is clearly a reciprocating pump.
A dirty exhaust and intense diesel knock from a C.I. engine is caused by
A)
High Cylinder temperature
B)
Poor Fuel Atomization
C)
Supplying insufficient fuel to suit the air
D)
Breaking up-the-injected fuel into very fine particles
In a Compression Ignition (C.I.) engine, the fuel is injected into the compressed hot air. For efficient combustion, the fuel must be atomized into very fine droplets to ensure a high surface-area-to-volume ratio, allowing for rapid evaporation and mixing with air.
1. Why 'Poor Fuel Atomization' is correct: If atomization is poor, large droplets of fuel are formed. These droplets take longer to evaporate and burn. This leads to an increased 'ignition delay' period. During this delay, more fuel accumulates in the cylinder. When combustion finally starts, this accumulated fuel burns almost instantaneously, causing a sudden pressure rise (Diesel Knock). Furthermore, the large droplets often fail to burn completely, leading to incomplete combustion, which manifests as 'dirty exhaust' (black smoke/soot).
2. Why other options are incorrect:
- (a) High Cylinder temperature: Generally reduces ignition delay and promotes smoother combustion, reducing knock.
- (c) Supplying insufficient fuel: This would lead to a lean mixture and loss of power, but would not typically cause intense knocking or dirty (sooty) exhaust.
- (d) Breaking up the injected fuel into very fine particles: This is the definition of good atomization, which prevents knock and ensures clean exhaust.
A single cylinder, 4-stroke engine is rotating at 1000 rpm. The number of power strokes occurring in one minute is
A)
500
B)
1000
C)
1500
D)
2000
Step-by-step calculation:
1. **Understand the Engine Cycle**: In a 4-stroke engine, one complete cycle consists of four strokes (Intake, Compression, Power, and Exhaust).
2. **Crankshaft Rotation**: One complete 4-stroke cycle requires two full revolutions of the crankshaft (720 degrees).
3. **Power Stroke Frequency**: Since there is only one power stroke per cycle, a 4-stroke engine produces one power stroke for every two revolutions of the crankshaft.
4. **Given Data**: The engine is rotating at 1000 rpm (revolutions per minute).
5. **Calculation**:
Number of power strokes per minute = (Engine Speed in rpm) / 2
Number of power strokes per minute = 1000 / 2 = 500.
Therefore, option (a) is correct. Options (b), (c), and (d) are incorrect because they do not account for the fact that a 4-stroke engine only fires once every two revolutions.
Refrigerant usually used in refrigeration in aeroplane
A)
Co2
B)
Air
C)
Freon
D)
None of these
In aircraft refrigeration systems, 'Air' is the primary refrigerant used. This is achieved through the 'Air Cycle Refrigeration System' (also known as the Bell-Coleman cycle or Reverse Brayton Cycle). Air is chosen for several critical reasons: 1. Weight: Using air eliminates the need for heavy compressors and condensers required by vapor compression systems. 2. Availability: Air is readily available from the engine's compressor (bleed air). 3. Safety: Air is non-toxic and non-flammable, which is crucial in the confined space of an aircraft cabin. 4. Simplicity: The system uses a heat exchanger and an expansion turbine to cool the air rapidly.
Why other options are incorrect:
- a. CO2: Too heavy and requires high pressure, making it unsuitable for aviation.
- c. Freon: While used in ground-based refrigeration, Freons are heavy and pose leakage risks that are dangerous in high-altitude pressurized cabins.
Formula for calculating horse power per ton of refrigeration
A)
4.75 / Cop
B)
475 / Cop
C)
47.5 / COP
D)
None of these
To derive the formula for Horse Power (HP) per Ton of Refrigeration (TR), we use the definition of the Coefficient of Performance (COP) and the conversion factors for power and refrigeration capacity.
1. **Definitions**:
- 1 Ton of Refrigeration (TR) = 3.517 kW (approximately 3.5 kW).
- 1 Horse Power (HP) = 0.746 kW.
- COP = (Refrigeration Effect) / (Work Input) = (Cooling Capacity) / (Power Input).
2. **Derivation**:
- Power Input (kW) = (Cooling Capacity in kW) / COP
- For 1 TR: Power Input (kW) = 3.517 / COP
3. **Convert Power from kW to HP**:
- Power Input (HP) = (Power Input in kW) / 0.746
- Power Input (HP) = (3.517 / COP) / 0.746
- Power Input (HP) = (3.517 / 0.746) / COP
- Power Input (HP) ≈ 4.715 / COP
4. **Conclusion**:
Rounding to the nearest standard option provided in technical exams, 4.715 is approximately 4.75. Therefore, the formula is HP/TR = 4.75 / COP.
- Option (a) 4.75 / Cop is the correct approximation.
- Option (b) 475 / Cop and (c) 47.5 / COP are mathematically incorrect by orders of magnitude.