Attempt the ISRO Mechanical & Aerospace 2020 previous year paper in real CBT exam mode or practice mode with verified answers and explanations.
All ISRO Mechanical & Aerospace papers
80 questions. Answers are shown only where the official answer key is available.
A centrifugal pump having an impeller diameter of 127 mm, delivers a power of 12 hp. If the impeller diameter is changed to 254 mm, what is the power, if other parameters are kept constant?
Answer: D. 96 hp
In a circular tube of diameter 100 mm and length 13 m with laminar flow, the friction factor is estimated to be 0.05. Calculate the Reynolds number?
Answer: C. 1280
A hot fluid is flowing through a long pipe of 4 cm outer diameter and covered with 2 cm thick insulation. It is proposed to reduce the conduction heat loss to the surroundings to one third of the present rate by increasing the same insulation thickness. The additional thickness of insulation required will be
Answer: D. 12 cm
Explanation: For cylindrical surface $Q \propto 1 / \ln(r_{out}/r_{in})$. $Q_2/Q_1 = 1/3$. $r_1 = 2$cm, $r_2 = 4$cm. Solving logarithmic relation, $r_3 = 16$cm. Increment = $16 - 4 = 12$ cm.
For a non-dimensional specific speed value of 1, for maximum efficiency, which of the following turbines is preferred?
Answer: B. Francis turbine
An experiment is conducted with a fluid of density 1 kg/m³ at 10 m/s velocity. The free stream static pressure is 100 kPa and the local static pressure is 101 kPa. What is the pressure coefficient at the location?
Answer: C. 20
An open tank is filled with water to a height of 20 m. What is the velocity of the water flow at the outlet, if the outlet is at the base of the tank?
Answer: B. 20 m/s (approx.)
Which of the following is a non-Newtonian fluid?
Answer: D. None of the above
A hot body at 1000 K transfers 2000 kJ of heat to a body at 500 K. Determine the net entropy change?
Answer: C. +2 kJ/kg
Highest ratio of specific heat is possible for?
Answer: A. Argon
Which of the following can be used to determine the variation of saturation pressure with temperature along phase boundaries?
Answer: D. Clausius- Clapeyron relation
Air at 27 °C and 100 kPa enters in a steady flow nozzle at a velocity of 100 m/s. If the inlet area of the nozzle is 0.5 m², what is the mass flow rate through the system?
Answer: C. 58 kg/s
Critical point of water is
Answer: B. 22.06 MPa
In a shower mixer, cold water at 27 °C, flowing at 5 kg/min is mixed with hot water at 77 °C flowing at 15 kg/min. The exit temperature of the mixture is
Answer: B. 64.5 °C
Which of the following uses a regenerator?
Answer: D. Both (b) and (c)
Ratio of convective mass transfer to the mass diffusion rate is called?
Answer: A. Sherwood number
A gas is contained in a cylinder with a moveable piston of 100 kg mass. When 2500 J of heat flow into the gas, the internal energy of the gas increases by 1500 J. What is the distance through which the piston rises?
Answer: B. 1 m
A refrigerator with COP of 5 is used in a room at 300 K. What will be the heat intake through a section of refrigerator wall of area 100 cm x 100 cm with a thickness of 10 cm, assuming only conduction? Value of thermal conductivity of the wall can be taken as 1 W/cm. K
A mass of 1 kg of air at 27 °C and 0.98 atm is taken through a diesel cycle. If the compression ratio of the engine is 16, calculate the temperature of the air after compression? (for calculation, take the ratio of specific heats of air as 1.5)
Answer: C. 927 °C
An aircraft is in its take off roll at sea level with ambient temperature of 18 °C. What is the approximate speed of the aircraft if the temperature measured by a probe at the exit of the engine diffuser is 36 °C? (Assuming air stagnation at diffuser outlet and Cp of air as 1.0 kJ/kg.K)
The external surface of a wall of 3 m height, 5 m width and 0.5 m thickness is at a temperature of 2 °C. If a heat loss of 150 W from the room is measured across the wall, find the inner wall temperature? The thermal conductivity of wall material can be taken as 1 W/m.K
Answer: A. 280 K
The typical range of Prandtl number for water is
Answer: B. 1.7-13.7
Analogy between momentum and heat transfer is known as
Answer: C. Chilton-Colburn analogy
Which of the following statement is true for a Rayleigh flow at M=1?
Answer: B. Entropy is maximum
A fluid passes through a well insulated tube of 4.7 cm² cross section area and 5 m length. If the pipe friction coefficient is 0.07 and the flow velocity is 3 m/s, then the flow can be represented using?
Answer: D. Fanno flow model
A fluid having a density of 1 g/cc is in a state with Grashof number 2 x 10^6 and prandtl number 0.7. Assuming acceleration due to gravity as 10 m/s², calculate the Rayleigh number?
Answer: A. 1.4 x 10^6
A cold liquid enters a counter flow heat exchanger at 15 °C at a rate of 8 kg/s. A hot stream of the same liquid enters the heat exchanger at 75 °C at 2 kg/s. Assuming the specific heat of the fluid as 4 kJ/kg °C. determine the maximum heat transfer rate.
Answer: D. 480 kW
The temperature of a surface with 0.2 m² area is 17 °C. Calculate the wavelength corresponding to maximum monochromatic emissive power
Answer: C. 10 micrometers
For a surface, the direct and diffuse components of the solar radiation are 400 and 300 W/m² and the direct radiation makes 60 deg angle with the normal. If the surface temperature is 300 K and effective sky temperature is 200 K, calculate net rate of radiation heat transfer. (Assume solar absorptivity and emissivity as 0.1 each; For calculation take Stefan Boltzmanns constant as 6 x 10^-8 W/m².K^4)
Answer: A. 11 W/m²
Which of the following element is added to high speed tool steels as a scavenger to remove slag impurities during melting and also for increasing cutting efficiency of tools.
Answer: B. Vanadium
Region of disorder created by movement of dislocations in super lattice is called:
Answer: C. Anti-phase boundary
The state of stress during deep drawing forming operation of a cup is
Answer: C. In the flange of the blank, bi-axial tension and compression and in the wall of cup, simple uni-axial tension
During turning of a metallic rod at a given condition, the tool life was found to decrease from 100 min to 25 min. When cutting speed was increased from 50 m/min. to 100 m/min. How much will be life of tool if machined at 80 m/min.?
Answer: B. 39.06 min.
In a single pass rolling operation, the thickness of a 100 mm wide plate is reduced from 20 mm to 15 mm. The roller radius is 125 mm and rotational speed is 8 rpm. The average flow stress for the plate material is 400 MPa. The power required for rolling operation in kW is?
Answer: D. 20 pi/3
A dummy activity is used in PERT network to describe
Answer: A. Precedence relationship
In small castings, which of the following allowances can be ignored.
Answer: B. Rapping Allowance
In an arc welding process, two weld coupons were made using two different welding processes. For the first coupon, the voltage, current and welding speed used are 15V, 300 A and 30 mm/min respectively. Whereas the second coupon is welded with 60 kV, 200 mA and 25 mm/s. If the heat transfer efficiency for welding the first coupon is half of that of second coupon, the ratio of heat input per unit length is?
Answer: B. 75:8
In Gas tungsten arc welding (GTAW) which of the following polarity is generally used for getting higher penetration
Answer: A. Direct current straight polarity (DCSP)
The laws of adhesive wear, commonly referred to as Archard's law can be expressed as (If 'Q' is the total volume of wear debris produced, 'W' is the normal load, 'L' is the sliding distance, 'H' is the hardness of the softest contacting surfaces being worn away, and 'k' is a non-dimensional wear coefficient dependent on the materials in contact and their exact degree of cleanliness)
Answer: A. Q = kWL/H
In a four-bar linkage if 'S' is the length of the shortest link, 'L' is the length of longest link and 'P' & 'Q' are length of other links, then the criteria for getting a triple rocker mechanism in which no links will fully rotate is
Answer: D. S+L > P+Q
The piston of an engine moves with simple harmonic motion. The crank rotates at 120 r.p.m. with a stroke of 2 meters. The velocity of the piston, when it is at a distance of 0.8 metre from the center is
Answer: B. 2.4 pi
If a block slides outward on a link at a uniform rate of 30 m/s, while the link is rotating at a constant angular velocity of 50 rad/s counter clockwise, the Coriolis component of acceleration is m/s².
Answer: C. 3000
In a screw jack of lead angle alpha, the effort required to lift the load W is given by (phi = Friction Angle)
Answer: B. P = W tan(alpha + phi)
When the axis of first and last gear are co-axial, then gear train is known as
Answer: C. reverted gear train
A disc spinning on its axis at 20 rad/s will undergo precession when a torque 100 N-m is applied about an axis normal to it. If the mass moment of inertia is 1 kg-m², then the angular velocity of precession is?
Answer: B. 5 rad/s
Which of the following is an absorption type dynamometer?
Answer: A. Prony brake dynamometer
Which of the following mechanism provides intermittent rotary motion?
Answer: B. Geneva Mechanism
If m,n are integers and m+n is odd then value of integral from 0 to pi of sin(mx) * cos(nx) dx is
1 + x + (x²)/2 - (x^4)/8 - (x^5)/15 + ........ =
Answer: C. e^(sin x)
The Laplace transform of $e^{at} \cos(\omega t)$
Answer: A. (s-a) / ((s-a)^2 + w²)
if u = yzi + 3zxj + zk, then curl u is
Answer: A. -3xi + yj + 2zk
cos(z) can be expressed as
Answer: A. 1/2 (e^(iz) + e^(-iz))
In a vector field, Divergence of the gradient is
Answer: D. Laplacian
If a continuously differentiable vector function is the gradient of a scalar function, then its curl is
Answer: D. zero
What does 'a' and 'e' indicate in the surface texture symbol shown below
Answer: A. Roughness value, machining allowance
Two steel trusses, XY and YZ of identical size supports a load of 200 N as shown in fig. The length of the truss in 1m. The force in the truss xy in N is
Answer: B. 200 N
A block weighing 100 N is resting on a plane inclined with horizontal as shown in Fig. What horizontal force P is necessary to hold the body from sliding down the plane? (Coefficient of friction can be taken as 0.25)
Answer: C. 60 N
The ratio of maximum shear stress to average shear stress in a beam of rectangular section is
Answer: C. 3/2
A mass less beam has a loading pattern shown in figure. Find the bending moment at mid span?
Answer: A. 1 kN-m
Steel machine element at the critical section is in biaxial stress state with two principal stress being 300 N/mm² and 300 N/mm² (equal magnitude). Find the von Mises stress (in N/mm²) in the member
Answer: D. 300
A machine component of 90 kg mass needs to be held in position using three springs as shown below. The spring constants K1, K2 and K3 are 4, 4 and 8 N/m respectively. Find the natural frequency of the system in rad/sec.
Answer: A. 0.33
A cylindrical pressure vessel has diameter 200 mm and thickness 2 mm. Find the hoop and axial stress (N/mm²) in the cylindrical vessel, when it is subjected to an internal pressure of 5 MPa.
Answer: D. 250, 125
For a long slender column of uniform cross section, the ratio of critical buckling load for the case with both ends hinged to the case with both ends clamped is
Answer: A. 0.25
If the length of a column subjected to compressive load is increase by three times its original length, the critical buckling load becomes
Answer: C. 1/9 of the original value
A square bar of size 10 mm x 10 mm and length 1000 mm is subjected to 200 N axial tensile force. The bar is made of mild steel having modulus of elasticity of 200 GPa. Find the strain energy density stored in the bar under this state of loading?
Answer: A. 10 J/m³
A solid circular shaft needs to be designed to transmit a torque of 55 N m. If the allowable shear stress of the material is 280 N/mm², find the diameter (in mm) of the shaft required to transmit torque. (Assume, pi = 22/7)
Answer: B. 10
If S is the applied stress, c is the width of the crack and r the radius of curvature at the tip of the crack, Griffith's crack theory gives the concentrated stress Sc as
Answer: A. 2S(c/r)^(1/2)
A metal alloy machine component is subjected to fluctuating tensile stress from 100 N/mm² to 200 N/mm². The material has yield and endurance strength of 450 and 200 N/mm² respectively. Find the factor of safety of the machine component.
Answer: B. 12/7
A driver of mass 100 kg is standing at the tip of a spring board of negligible mass. The natural frequency of the spring board with the driver is 1.6 Hz. What is the static deflection at the tip of the spring board when the driver is standing at the tip?
Answer: C. 98.1 mm
Which of the following is classified as a secondary bond in materials?
Answer: D. Hydrogen bonding
The number of atoms per unit cell for an FCC crystal structure is
Answer: B. 4
Which of the following hardness test uses diamond cone type indenter?
Answer: D. Rockwell
In a two component system, if the non-compositional variable is only temperature, the number of degrees of freedom in the case of a single phase field as per Gibbs Phase Rule is?
Answer: C. 2
In an iron-carbon diagram, the percentage by weight of carbon at eutectoid composition is
Answer: B. 0.76
Of the various microstructures that may be produced for a given steel alloy, which among the following is the hardest form
Answer: A. Martensite
Which spring steel is widely used for aircraft engine valves
Answer: B. Chrome vanadium
If, Kf is the fatigue stress concentration factor and Kt is the theoretical stress concentration factor then, the notch sensitivity q is?
Answer: B. (Kf-1)/(Kt-1)
Beach or clamshell marks on a failed metallic surface are typical of
Answer: D. Fatigue failure
In vibration isolation if $\omega/\omega_n$ is less than $\sqrt{2}$ then the transmissibility will be
Answer: C. Greater than one
The natural frequency of a simply supported beam of length l with mass M at its centre, flexural rigidity EI and negligible beam mass is
Answer: A. 1/(2*pi) * $\sqrt{48EI/Ml³}$
A machine component of natural frequency 20 rad/s is subjected to a base motion from the machine which is harmonic in natural with amplitude 3 m/s² at 10 rad/s. What is the peak amplitude of relative displacement of the components if the damping is negligible?
Answer: C. 10.0 mm