UPSSSC JE Mechanical Paper 2 Mock Test - 4 - Mechanical Engineering MCQ

Advantages of Forging

• Mechanical properties and reliability of the materials increase due to the improvement in the crystal structure.

• Forging reduces the grain size of the metal, which increases strength and toughness.

• Fatigue and creep strength increases

• Improved physical property

Disadvantages of Forging

• Tooling cost in forging is more

• Poor dimensional accuracy and surface finish

• Forging operations are limited to simple shapes and have limitations for parts having undercuts, re‐entrant surfaces, etc.

If the radius of the addendum circle of the wheel increases beyond a limiting value, then the tip of a tooth on the wheel will cause interference with the tooth on the pinion and vice versa.

Interference may only be prevented if the addendum circles of the two mating gears cut the common tangent to the base circles between the points of tangency.

If the addendum for gear and pinion are to be equal, the addendum radius of the wheel decides whether the interference will occur or not. Because the addendum circle of the wheel passes through the limiting point on the line of action (interfering with the pinion) before the addendum circle of the pinion passes through the limiting point on the same line. So, in this case, the chances of interference are more for the wheel than the pinion. Here the tip of the wheel will undercut the flank of the pinion.

The efficiency of a centrifugal pump will be maximum when the blades are bent backward.

△Q1 =100k Trang≤W1=50kj

△Q2=120kjW2=?

The given process is a cyclic process Hence △U=0

⇒△Q1+△Q₂=△W₁+△W₂

100+120=50+△W₂

△W₂ = 170kj

Therefore for completing the one thermodynamic cycle (power cycle), the piston has to complete two strokes only those are one upward and downward movement. Thus the crankshaft completes only one revolution during the completion of the power cycle.

Carnot cycle is one of the best-known reversible cycles. The Carnot cycle is composed of four reversible processes.

• Reversible Isothermal Expansion (process 1-2)
• Reversible adiabatic expansion (process 2-3)
• Reversible isothermal compression (process 3-4)
• Reversible adiabatic compression (process 4-1)

Fig. P-V and T-S diagrams of Carnot Cycle

The transmission angle is the angle between the output link and the coupler. If the value of the transmission angle is zero, then the mechanism will lock or jam. If the transmission angle deviates from the 90^O, then the torque on the output link decreases. So usually, the value of this angle is kept at more than 45^O. The best mechanism is in which the transmission angle does not deviate much from the 90^O.

The tools used in planing and shaping are similar to single-point lathe tools, consisting of the shank and the point.

Planing and shaping tools are made of HSS or tipped with cemented carbides.

For Uniform wear theory, the mean radius of friction surface is given as

Basic Principle of Hot Wire Anemometer

When an electrically heated wire is placed in a flowing gas stream, heat is transferred from the wire to the gas, and hence the temperature of the wire reduces, and due to this, the resistance of the wire also changes. This change in opposition of the wire becomes a measure of flow rate.

∴ A hot wire anemometer is used to measure the velocity of the fluid.

The refrigerant enters at very low pressure and temperature after passing through the expansion valve in the evaporator. This refrigerant absorbs the heat from the substance that is to be cooled, so the refrigerant gets heated while the substance gets cooled. The refrigerant leaves the evaporator in the vapour state, mostly superheated, and is absorbed by the compressor. In the compressor, the temperature and pressure both increase. After the compressor, the refrigerant goes to the condenser, where its temperature decreases while pressure is constant. So in the entire cooling cycle, the pressure and temperature change.

Boiler Economiser ( Sometimes Called Economizer ) is the Energy improving device that helps to reduce the cost of operation by saving the fuel. In boilers, economizers are generally Heat Exchangers which are designed to exchange heat with the fluid, generally water.

Completely constrained motion is a type of constrained motion in which relative motion between the links of a kinematic pair occurs in a definite direction by itself, irrespective of the external forces applied.

Fixture results in faster and accurate machining with consistent quality, functional ability, and interchangeability.

A jig is a fixture with an additional feature of tool guidance.

Thus fixture does not guide the tool, and guiding is done with the help of Jig.

Mercury has a very low vapour pressure when compared to that of water. So, it is more sensitive than water to the changes in the atmospheric pressure and rises more quickly to record the changes in the atmospheric pressure.

In actual compressors, a small clearance is left between the cylinder head and piston to accommodate the valves and to take care of thermal expansion and machining tolerances.

A large clearance volume results in low volumetric efficiency and hence large cylinder dimensions increase the contact area between the piston and cylinder and so, increases friction and work.

Volumetric efficiency is given by:

Where c = Clearance ratio.

P₂/P₁=Pressure;ratio

As the clearance ratio increases, the volumetric efficiency of the reciprocating compressor decreases as the pressure ratio increases.

The pressure angle, representing the steepness of the cam profile, is the angle between the normal to the pitch curve at a point and the direction of the follower motion. It varies in magnitude at all instants of the follower motion. A high value of the maximum pressure angle is not desired as it might jam the follower in the bearings.

The positive clutches are used when a positive drive is required. The simplest type of a positive clutch is a jaw or claw clutch or dog clutch.

Friction Clutches: The force of friction is used to start the driven shaft from rest and gradually brings it up to the proper speed without excessive slipping of the friction surfaces. Example: Disc or plate clutches, Cone clutches, Centrifugal clutches.

- Intensive Property does not depend on the amount of matter; Example: Pressure, temperature

- Extensive property depends on the amount of matter. Example: Mass, Volume, Energy, etc.

- Intensive properties are independent of the mass in the system, while extensive properties are related to the mass; If the mass is increased, the value of the extensive properties also increases.

- Specific extensive properties i.e., specific volume, specific energy, etc. are intensive properties i.e., independent of the mass

The point ' M ' at which the line of action of the new buoyant force intersects the original vertical through the CG of the body is called the metacentre. It is a point about which a floating body starts oscillating when given a small angular displacement.

Equilibrium Position Tilted Position

GM > 0 (M is above G) Stable equilibrium

GM = 0 (M coinciding with G) Neutral equilibrium

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Pure torsion will be the case of pure shear in which principal normal stresses occur 45° to the axis.

Maximum and minimum principal stresses are equal in magnitude and opposite in direction.

2θ₁ = 90° ⇒ θ₁ = 45°

Octane number is the percentage of isooctane in the mixture of iso-octane and n-heptane. The octane number is for gasoline (petrol) fuel. Gasoline with an octane number of 80 means 80% of isooctane and 20% of n-heptane, i.e., the branched-chain alkane is more, so knocking is less.

According to the third law of motion: For every action, there is an equal and opposite reaction; Recoiling is the backward momentum of a gun to balance the forward momentum of the bullet.

thus, the unit of dynamic viscosity is N−s/m² or kg/(m.sec), and dimension is ML

⁻¹T⁻¹

If a set of pipes described by (L₁, D₁, f₁), (L₂,D₂,f₂)....... are connected in series then an
equivalent pipe (L_e, D_e,f_e) is related as