UPSSSC JE Mechanical Paper 2 Mock Test - 2 - Mechanical Engineering MCQ

Wet-bulb temperature (WBT): It is the temperature of air shown by a thermometer whose bulb is covered with a wet cloth.

Wet Bulb Depression (WBD): The difference between dry bulb temperature and wet bulb temperature.

WBD = DBT - WBT

Now WBD = 0

So DBT = WBT, which happens when the air is fully saturated. So the relative humidity is 100 %.

Process 1-2: Isentropic compression

Process 2-3: Constant volume heat addition

Process 3-4: Isentropic expansion

Process 4-1: Constant volume heat rejection.

Diesel cycle is a gas power cycle widely used in diesel engines. The diesel cycle is also known as a constant pressure cycle as heat is supplied at constant pressure.

In the Carnot cycle, heat is supplied and rejected at constant temperature expansion and compression, respectively.

The mass of an object can be calculated in a number of different ways: mass=density×volume (m=ρV). Density is a measure of mass per unit of volume, so the mass of an object can be determined by multiplying density by volume. mass=force÷acceleration (m=F/a).

∴ Weight of wooden block = Weight of the volume of fluid displaced

Let,

The density of wooden block = γ_b, the density of water = γ_w, and volume of block = V

Weight of wooden block = γ_b × V

Weight of the volume of fluid displaced = γ_w × 2/3 × V

γ_b × V = γw × 2/3 × V

∴ γ_b = 2/3 × γ_w

∴ The relative density for the wooden block is γb/γw = 2/3.

In the On-off control of the air-handling unit, the fan motor is operated intermittently by the room thermostat, the bulb of which is installed in the return air.

A thermostatic expansion valve maintains a constant degree of superheat at the exit of an evaporator; hence it is most effective for dry evaporators in preventing the slugging of the compressors since it does not allow the liquid refrigerant to enter the compressor.

The planes of maximum and minimum normal stresses are at an angle of 90° to each other.

Planes of maximum stress occur at 45° to the principal planes.

In a refrigerator, one removes heat from a lower temperature and deposits to the surrounding at a higher temperature. In this process, mechanical work has to be done, which is provided by an electric motor.

A thermistor, derived from the term thermally sensitive resistors, is a very accurate and cost-effective sensor for measuring temperature. It is available in 2 types, NTC (negative temperature coefficient) and PTC (positive temperature coefficient); it is the NTC thermistor that is commonly used to measure temperature.

For ν = 0.5 ⇒ ev = 0

The bulk modulus of elasticity measures the compressive stress per unit volumetric strain.

For incompressible fluid: dρ = 0 ⇒ dV = 0

For dV = 0 ⇒ k = ∞

A positive rake angle is used for cutting soft and ductile material.

A negative rake angle is used for cutting very hard or brittle material.

A zero rake angle is used for machining brass material.

A higher cutting force is required at a low positive rake angle, but with the increase of positive rake angle, a lesser amount of cutting forces and power is required, which gives a better surface finish. But the tool becomes thin and weak.

Thus, a hard material deforms less in the chip at a higher positive rake angle as the tool loses strength.

The rating indicates the maximum capacity of a boiler. When a boiler operates at its maximum rated capacity, it is referred to as the maximum load. If the load varies from hour to hour, it operates at a varying load. Load and load variations can influence the amount of chemicals required for treatment and the treatment controls required.

Cast iron = 10mm/m

Steel=20mm/m

Aluminium = 15mm/m

Brass =15 mm/m

Therefore steel needs highest pattern allowance. 

Stirling Cycle. Thermodynamically, the ideal Stirling cycle consists of isothermal compression, constant volume heat addition, isothermal expansion, and constant volume heat rejection. The Stirling cycle, without regeneration, is rather inefficient, but with effective regeneration, the system efficiency can be high.

The unit of momentum is the product of the units of mass and velocity. In SI units, if the mass is in kilograms and the velocity is in meters per second, then the momentum is in kilogram meters per second (kg⋅m/s).

SI unit: kilogram meter per second kg⋅m/s

The atomic nucleus is the small, dense region consisting of protons and neutrons at the center of an atom, discovered in 1911 by Ernest Rutherford based on the 1909 Geiger–Marsden gold foil experiment. Protons and neutrons are bound together to form a nucleus by the nuclear force.

It is used in calculating the heat transfer, typically by convection or phase transition between a fluid and a solid. The heat transfer coefficient has SI units in watts per squared meter kelvin: W/(m²K). The heat transfer coefficient is the reciprocal of thermal insulance.

Two-stroke engines often have a high power-to-weight ratio. Compared to four-stroke engines, two-stroke engines have a greatly reduced number of moving parts and so can be more compact and significantly lighter.

Important Point:

Two-stroke engines: In this engine, one power stroke is obtained in each revolution of the crankshaft

Four-stroke engines: In this type of engine, one power stroke is obtained in two revolutions of the crankshaft

PdA - (P + dP) dA - ρgdAds sin θ = 0

Assumptions in Bernoulli’s equation:

i) fluid is ideal

ii) flow is steady

iii) flow is continuous

iv) fluid is incompressible

v) flow is non-viscous

vi) flow is irrotational

vii) applicable along a streamline

Where,

= velocity head

= pressure head

z = elevation of datum head

= piezometric head

- The line representing the sum of all 3 head is known as the total energy line or total head line.

- Line joining the points of piezometric heads is known as hydraulic grade line or piezometric line.

Pressure Angle is the measure of the steepness of the cam profile. The angle between the direction of the follower movement and the normal to the pitch curve at any point is called pressure angle. Pressure angle varies from maximum to minimum during complete rotation.

The pressure should not exceed 30^० in the case of cams with translating followers (and angle should be less than 45^० for low-speed cam mechanisms with oscillating followers).

- Viscosity is the most important property of lubricating oil. It is a measure of its internal friction or resistance to flow.

- It provides a measure of the thickness of lubricating oil at a given temperature; the higher the viscosity, the thicker the oil.

Correct Answer :- a

Explanation : For 450 m head of water, Pelton wheel shall be used.

A Pelton turbine or Pelton wheel is a type of hydro turbine (specifically an impulse turbine) used frequently in hydroelectric plants. These turbines are generally used for sites with heads greater than 300 meters.

The water in a Pelton turbine is moving quickly and the turbine extracts energy from the water by slowing the water down, which makes this an impulse turbine.

a = mg( sin Ɵ - μ cos Ɵ ) The acceleration of the body down a rough inclined plane is always less than the acceleration due to gravity g. that is a < g. Thus, the minimum force required to push the body down the inclined plane is f (down) = mg(sin Ɵ + μ cos Ɵ)

Brake power/Shaft power is the power available at the engine crankshaft.

B.P = T × ω

Indicated Power is the power developed inside the cylinder of the engine.

I.P = P_mean× VS

Friction power is the power that losses due to bearing friction, pumping losses, and the power in driving the auxiliary devices like feed pump, valve mechanisms, ignition system, etc.

F.P = I.P – B.P

Slenderness ratio (λ)

Uncut chip thickness t₁=0.2mm

Cut chip thickness t₂=0.2mm

Chip thickness ratio