Essential Mechanical Interview Questions Part -10
Q – 111 What is meant by payload for aircraft?
Ans- The payload is the cargo that it carries.
Q – 112 Who invented the four-stroke engine?
Ans- Nikolavs August Otto, German
Q – 113 What was the spinning jenny?
Ans- The spinning jenny is a multi-spool spinning wheel. It was invented circa 1764 by James Hargreaves in Stanhill, near Blackburn, Lancashire in the north west of England (although Thomas Highs is another candidate identified as the inventor).
Q – 114 What is the formula for Heat loss in a pipe?
Ans- Pipes are generally cylindrical in structure of amount of heat loss through pipe is given by the formula
Q= 2 pi k L (T1-T2)/ln (r2/r1)
Where
k=conductivity of material of which pipe is made
T1= temperature of inside layer pipe
T2=temperature outside layer of pipe
L= length of pipe
r1= inner radius
r2=outer radius
ln=natural logarithm
pi=22/7
The above condition applies for steady state flow, single layer over cylinder and neglecting conductivity
To take conductivity into account term Q* must be added
Q*=2 pi L {r1 hi (Ti-T1) +r2 ho (T2-To)}
hi=convective coefficient for inside layer
ho=convective coefficient for outside layer
Ti= temperature of inside space of pipe
To=temperature of outside space of pipe
Q – 115 Why would you use hydraulics rather than pneumatics?
Ans- Hydraulics is suitable for higher forces & precise motion than pneumatics. This is because hydraulic systems generally run at significantly higher pressures than pneumatics systems. Movements are more precise (repeatable) because hydraulics uses an incompressible liquid to transfer power whilst pneumatics uses gases.
Pneumatic systems have some advantages too. They are usually significantly cheaper than hydraulic systems, can move faster (gas much less viscous than oil) and do not leak oil if they develop a leak.
Q – 116 What is a positive displacement pump?
Ans- A positive displacement pump causes a liquid or gas to move by trapping a fixed amount of fluid or gas and then forcing (displacing) that trapped volume into the discharge pipe. Positive displacement pumps can be further classified as either rotary-type (for example the rotary vane) or lobe pumps similar to oil pumps used in car engines. These pumps give a non-pulsating output or displacement unlike the reciprocating pumps. Hence, they are called positive displacement pumps.
Q – 117 What is enthalpy?
Ans- Enthalpy is the heat content of a chemical system.
Q – 118 What are the differences between pneumatics and hydraulics?
Ans-
* a) Working fluid: Pneumatics use air, Hydraulics use Oil
* b) Power: Pneumatic power less than hydraulic power
* c) Size: P components are smaller than H components
* d) Leakage: Leaks in hydraulics cause fluid to be sticking around the components. In pneumatics, air is leaked into the atmosphere.
* e) Pneumatics obtain power from an air compressor while hydraulics require a pump
* f) Air is compressible, hydraulic oil is not
Q – 119 What is a uniformly distributed load?
Ans- A UDL or uniformly distributed load is a load, which is spread over a beam in such a way that each unit length is laded to the same extent.
Q – 120 What is the main purpose of an airspeed indicator in an aircraft?
Ans- The primary purpose of an airspeed indicator in an aircraft is to give the pilot some sense of how fast the aircraft is moving. A pitot tube, which is a forward pointing hollow tube that is mounted on the plane, is pressurized by the force of the air the plane encounters as it flies. This air pressure is compared to a static reference, and the difference is proportional to the airspeed.
The faster the plane moves, the higher the pressure in the Pitot tube, and the greater the difference between that and the reference. All that will result in higher indicated air speed. There are some issues associated with the accuracy of the system (like when the plane is flying into a headwind), and information on. The pictures are informative, and a reader can pick up a handful of specialized terms relating to the device and the principles upon which it operates.
Q – 121 What is the full form of WCB in ASTM?
Ans- American Society for Testing and Matreails
Q – 122 Why is the suction pipe of vapor compression and refrigeration system insulated?
Ans- The vapor compression and refrigeration system is used to minimize sweating of the air around the pipe. When the air is exposed to a cool surface, its water vapor condenses.
Q – 123 What does F.O.F. stand for in piping design?
Ans- FOF stands for Face of Flange.
A flange has either of the two types of faces:
* a) Raised face
* b) Flat face
The F.O.F is used to know the accurate dimension of the flange in order to avoid the minute errors in measurement in case of vertical or horizontal pipelines.
Q – 124 What is the alloy of tin and lead?
Ans- A tin and lead alloy is commonly called solder. Usually solder is a wire with a rosin core used for soldering. The rosin core acts as a flux.
Q – 125 What is the gas constant R for air?
Ans- Air gas constant is Rair=R/28.97=0.2869 (J/g K) = 286.9 (J/kg K)
Q – 126 What are the thermal conductivity properties of brass?
Ans- 109 W/ (m*K) @ 300K
Q – 127 What is a cotter joint?
Ans- These types of joints are used to connect two rods, which are under compressive or tensile stress. The ends of the rods are in the manner of a socket and shaft that fit together and the cotter is driven into a slot that is common to both pieces drawing them tightly together. The tensile strength of the steel is proportionate to the strength needed to offset the stress on the material divided by the number of joints employed.
Q – 128 How does a Coal Power station produce electricity?
Ans- A fossil fuel power plant (FFPP) (also known as steam electric power plant in the US, thermal power plant in Asia, or power station in the UK) is an energy conversion center designed on a large scale for continuous operation. Just as a battery converts relatively small amounts of chemical energy into electricity for temporary or intermittent use, the FFPP converts the energy stored in fossil fuels such as coal, oil, or natural gas successively into thermal energy, mechanical energy, and finally electric energy for continuous use and distribution across a wide geographic area.
Usually, the coal is utilized to convert water into steam in boilers (thermal energy). The steam is then used to drive steam turbines (mechanical energy). The turbine shaft is coupled to a generator shaft, which generates electricity.
Q – 129 How does length and initial angle affect the period in a simple pendulum?
Ans- The longer the pendulum is the greater the period of each swing. If you increase the length four times, you will double the period.
It is hard to notice, but the period of a pendulum does depend on the angle of oscillation. For small angles, the period is constant and depends only on the length of the pendulum. As the angle of oscillation (amplitude) is increased, additional factors of a Taylor approximation become important. (T=2*pi*sqrt (L/g) [1+theta^2/16+…] and the period increases.
Interestingly, if the pendulum is supported by a very light wire then the mass of the object at the end of the pendulum does not affect the period. Obviously, the greater the mass, the less any air friction, or friction at the pivot will slow the pendulum. Also interestingly, the pendulum period is dependant on the force of gravity on the object (g). One must not assume that g is constant for all places on Earth.
Q – 130 What is jet plane?
Ans- An aircraft powered by a jet engine.
Q – 131 What is the difference between the flight of a plane and a helicopter?
Ans- Both use the pressure difference caused by air moving over the wings at different speeds to generate lift a plane by moving those wings in the direction of travel, a helicopter by spinning the “wings” around at high speed.
Q – 132 Is shear thinning fluids and the linear viscoelastic fluids are the same?
Ans- No
Q – 133 What is the difference between projectile motion and a rocket motion?
Ans- A projectile has no motor/rocket on it, so all of its momentum is given to it as it is launched. An example of a projectile would be pen that you throw across a room.
A rocket or missile does have a motor/rocket on it so it can accelerate itself while moving and so resist other forces such as gravity.
Q – 134 What is ferrite?
Ans- Magnetic iron rock
Q – 135 What is the difference between shear center flexural center of twist and elastic center?
Ans- The shear center is the centroid of a cross-section. The flexural center is the center of twist, which is the point on a beam that you can add a load without torsion. The elastic center is located at the center of gravity. If the object is homogeneous and symmetrical in both directions of the cross-section then they are all equivalent.
Q – 136 What kinds of pipes are used for steam lines?
Ans- Normally galvanized pipes are not used for steam. Mild steel with screwed or welded fittings are the norm. Pressure and temperature are very important factors to be considered in what type of materials to be used. Steam even at low pressures can be extremely dangerous.
Q – 137 What is a pneumatic system?
Ans- Pneumatic system is a system that uses air to power something. For instance, have you seen the tube systems at bank drive-up tellers? Air is used to push the tubes back and forth from the teller to the customer.
Air is also used to power drills, sanders, grinders, and the like at garages and car body shops.
Q – 138 Where do you put the oil in a compressor?
Ans- In the reciprocating compressors, you fill the crankcase with the lubricante.
In screw compressors, there is a reservoir to separate oil from compressed air, that reservoir works as the oil sump of the screw compressor.
Q – 139 Does the position of a chicken egg affect the amount of weight it can withstand?
Ans- Yes. Lying on its side, it will break with very little pressure. That is why, when you break an egg, you always strike the side.
Q – 140 How do you repair a hydraulic jack?
Ans- In general, it seems simple: polishing scored cylinders and pistons, replacing worn seals, replacing excessively worn or damaged parts, etc. However, for an ordinary person, the problem I have run into is finding a readily accessible source of parts, as the hydraulic repair industry seems to be a closed fraternity.
Q – 141 If the black box flight recorder is never damaged during a plane crash, why not the whole airplane made out of that stuff?
Ans- The SR-71 was made mostly out of Titanium (very high strength to weight ratio) and it got off the ground fine. In addition, a two-seat airplane cost $33 million in 1960s dollars, so no one would ever be able to afford an airliner made out of it.
Q – 142 How do motion detectors work?
Ans- Motion detectors work to help with construction work.
Q – 143 How do you determine what suction pressure should be in R22 air conditioning compressors suction line?
Ans- The type of refrigerant used and sometimes the amount of charge determines the proper suction pressure of any air conditioning or refrigeration system.
Q – 144 What are the minerals needed to make or build a car?
Ans- * a) Sulfur is used in tire construction
* b) Aluminum and iron in the car body and engine
* c) Quartz is used in windshield construction
* d) Chromium is used for chrome plating
* e) Copper is used in wiring
* f) Magnesium may be used in the wheels
* g) Zinc would be used in rust plating
* h) Gold may be used in the spark plugs and in electrical connections
* i) Tin may be used in solder
* j) Lead will be used in the batteries
* k) Tungsten may be used in the light bulb filaments
Q – 145 Is it possible for something to explode in space like in the movies?
Ans- Yes, provided there is an oxygen source. A spaceship with liquid hydrogen and liquid oxygen will blow up quite well in the vacuum of space. Chemical explosives will also explode in space since they function by breaking weakly bonded chemical components; no oxygen is necessary. Nuclear explosions can of course occur in space, too. The United States military in the 60’s performed a series of nuke tests in outer space, and found out what EMP can do, when they briefly wiped out Hawaii’s electrical grid for a few hours.
Q – 146 What is a feasibility study?
Ans- In order to make wise investments in a marketplace experiencing increasing levels of risk, companies are turning to feasibility studies to determine if they should offer new products, services or undertake a new business endeavor. The purpose of a feasibility study is to determine if a business opportunity is possible, practical, and viable. When faced with a business opportunity, many optimistic people tend to focus on just the positive aspects.
A feasibility study enables a realistic view at both the positive and negative aspects of the opportunity. A feasibility study is an important tool for making the right decisions. A wrong decision often leads to business failure. For example, only 50% of start-ups are still in business after 18 months and only 20% are in business after 5 years.