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UPSC | GATE Exam for Mechanical | Objective Question and Answers | Tamilnadu Teachers Recruitment Board

Objective Question and Answers for UPSC / GATE Exams:

UPSC | GATE Exam for Mechanical | Objective Question and Answers | Tamilnadu Teachers Recruitment Board

The common soldering method used for soldering circuit components to their boards is known as:
  1. WAVE soldering
  2. Reflow soldering
  3. Furnace soldering
  4. Infrared soldering
Answer:

WAVE soldering

Hint:

Wave soldering is a large-scale soldering process by which electronic components are soldered to a printed circuit board (PCB) to form an electronic assembly. The name is derived from the use of waves of molten solder to attach metal components to the PCB.

Re-flow soldering is a process in which a solder paste (a sticky mixture of powdered solder and flux) is used to temporarily attach one or several electrical components to their contact pads, after which the entire assembly is subjected to controlled heat, which melts the solder, permanently connecting the joint.

Infrared Soldering by soldering individual joints with a hot air pencil.


The heat generated in metal cutting is dissipated in different proportions in to environment, tool, chip and work piece. The correct order of this proportion in descending magnitude is (no cutting fluid is used):
  1. Tool, work, chip, environment
  2. Work, tool, chip, environment
  3. Tool, chip, environment, work
  4. Chip, tool, work, environment
Answer:

Chip, tool, work, environment

Hint:

The maximum temperature in the cutting zone occurs not at the tool tip but at some distance further up the rake face. Material at a point (Chip) gets heated as it passes through the shear zone and finally leaves the chip. The point at built up edge, heating continues beyond the shear plane into the frictional heat region. So tool is the next highest absorbing medium. The point nearer to work their temperature rises merely due to conduction of heat into the work piece.


 

Flatness of slip gauges is checked with:
  1. Optical flat
  2. Electronic comparator
  3. Interferometer
  4. Linear measuring machine
Answer:

Electronic comparator

Hint:

For flatness measurement of surfaces the easiest and best way to test is with an optical flat. Normally Slip gauges and angular measuring instruments are used for accurate measurements of flatness in surface. Here the work piece and Optical flats are hold each other and a monochromatic lights are passed in between the gap. If the light bands visible then the surfaces are not in perfect contact.

In this question flatness of slip gauge are checked. So we need a high precisioned electronic comparator to check the flatness surface in slip gauges.

Interferometers are non contact type flatness measurement of surfaces such as thin, transparent wafers, substrates and windows.


The flatness of a machine bed can be measured using:
  1. Auto collimator
  2. Vernier calipers
  3. Height gauge
  4. Tool maker’s microscope
Answer:

Height gauge

Hint:

Flatness is can be measured using a height gauge run across the surface of the part if only the reference feature is held parallel.

Autocollimator is an optical instrument which is used to measure small angles with very high sensitivity. Normally straightness measured with autocollimator.

Tool maker’s microscope used for length, angle, Thread, and straightness measurements.


In a turbulent boundary layer over the entire length of a plate, the boundary layer thickness increase with its distances ‘X’ from the leading edge is:
  1. X1/2
  2. X1/5
  3. X2/5
  4. X4/5
Answer:

X4/5

Hint:

ρ α X (1 / 2)

When the fluid flows this cohesive force along with adhesion shows itself in the macroscopic scale as viscosity. As the flow proceeds downstream of the flat plate the viscosity is able to slow down more and more fluid layers above the flat plate. This is what is called momentum transfer. And hence the boundary layer thickness increases as the fluid moves downstream.


 

The continuity equation (du/dx)+ (dv/dy)=0 is valid for:
  1. Ideal fluid flow only
  2. In-compressible fluids, the flow may be steady (or) unsteady
  3. Steady flow, the flow may be compressible (or) in-compressible
  4. In-compressible fluids and steady flow
Answer:

In-compressible fluids, the flow may be steady (or) unsteady

Hint:

In-compressible flow means  du/dx+dv/dy=0, Some time du/dx = 0 and dv/dy = 0. So the flow may be steady or unsteady.

Teachers Recruitment Board Tamilnadu Multiple Choice Questions for Mechanical Engineering

No cutting fluid is used in the following operation:
  1. Planning and shaping
  2. Broaching
  3. Honing
  4. Thread rolling
Answer:

Planning and shaping

Hint:

In planning and shaping operation, cast iron work piece machined. Graphite in the cast iron acts as a lubricant in itself. But machining cast iron will get you fine powders everywhere that tend to sneak into your machines nooks and corners and get lodged there. The stuff later becomes very difficult to remove especially after mixing up with machine lube or oil.

 

Which one of the following is not a decision taken during the aggregate production planning stage?
  1. Scheduling of machines
  2. Amount of labour to be committed
  3. Rate at which production should happen
  4. Inventory to be carried forward
Answer:

Scheduling of machines

Hint:

The aggregate planning is particularly useful for organizations that experience seasonal or other fluctuations in demand or capacity. Planners must make decisions on output rates, employment levels and changes, inventory levels and changes, back orders, and subcontracting. So Aggregate production planning is a short term decision making process.

  • It is usually possible to
  • hire or lay off workers
  • increase or decrease number of shifts
  • increase / decrease number of working days in a week
  • decrease or increase working hours (overtime or under time)
  • subcontract work to other firms
  • build up or deplete inventory levels

 

Which of the following is incorrect regarding template in layout design?
  1. Templates are three dimensional representation of machines (or) equipments
  2. Templates are virtual picture of layout
  3. Templates are used for storage areas
  4. Templates shows the area occupied by machine
Answer:

Templates are three dimensional representation of machines (or) equipment’s

Hint:

Two dimensional plan – Templates

Three dimensional plan – Miniature Models

 

Arrival rate of telephone calls to a telephone book is 9 minutes between two consecutive arrivals and length of the telephone call is assumed to be exponentially distributed with mean 3 minutes. The probability that a person will have to wait:
  1. 33
  2. 333
  3. 33
  4. 33
Answer:

0.333

Hint:

Here, N and Nq are the number of people in the system and in the queue respectively. Also W and Wq are the waiting time in the system and in the queue respectively. ρ is the ratio of arrival rate to service rate. Also the probabilities can be given as :

where, p0 is the probability of zero people in the system and pk is the probability of k people in the system.

Given:

Arrival rate λ = 1/9 minutes

Service rate μ = 1/3 minutes.

Probability that a person will have to wait

= (1/9)/(1/3) = 0.333

A dummy activity is used in PERT network to describe:
  1. Precedence relationship
  2. Necessary time delay
  3. Resource restriction
  4. Resource idleness
Answer:

Precedence relationship

Hint:

A CPM/PERT network consists of branches and node. The arrows in between the nodes indicated the precedence relationships between activities. A dummy activity inserted into the network to show a precedence relationship, but it does not represent any actual passage of time.

 

Slow cooling rate in solidification of casting results in:
  1. Fine dendrite with large arm spacing
  2. Coarse dendrite with large arm spacing
  3. Coarse dendrite with smaller arm spacing
  4. Fine dendrite with smaller arm spacing
Answer:

Coarse dendrite with large arm spacing

Hint:

Solidification mechanism is essential for preventing defects due to shrinkage. During solidification, cast forms develops cohesion and acquires structural characteristics. Since heat loss is more rapid near the mold walls than any other place, the first metal crystallizes called ‘nuclei’. Slow cooling makes the dendrites to grow long whereas fast cooling causes short dendrite growth. So slow cooling results in larger grain structure and fast cooling results in small grain structure in the solidified metal.