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ISRO Mechanical Engineering Heat Transfer Questions, Answers and Explanation Conduction 2017.2.62.  The distribution of a temperature T, at a particular instant , across a large concrete wall, 1m thick, which is heated from one side is given by the equation T = 150-80x+16x 2 , where the distance x is in meters and T is in degree Celsius. Thermal conductivity of wall is 0.6W/mK, area of cross section is 10 m 2 . The heat accumulated in unit time at this instant in the concrete wall is a) 768J/sec b) 384J/sec c) 96J/sec d) 192J/sec Answer d) 192J/sec Explanation Heat accumulated = Heat conducted away - Heat conducted in Q = kA*[dT/dx] at x = 1 minus at at x = 0 = 0.6*10*(-80+32x) at x = 1 minus at x = 0 =6*32 = 192J/sec General 2017.2.29.  Which of the following is FALSE? a) Heat flow by conduction is directly proportional to the area and temperature gradient b) Heat flow by convection is directly proportional to the area and temperature differen...

ISRO 2015 Mechanical Engineering Questions, Answers and Explanation 11. Which of the following is applied to brittle materials? a) maximum principal stress theory b) maximum principal strain theory c) maximum strain energy theory d) maximum shear stress theory Answer a) maximum principal stress theory Explanation [ Strength of Materials ] Ductile Materials - Planes of maximum shear exist in the material at 45 o and the material begins to slide along these planes. Maximum shear stress theory/ Total strain energy theory can be used. Brittle Materials - When the normal stress in the material reaches the ultimate stress the material fails suddenly by fracture. Maximum principal stress theory can be used.

ISRO 2013 Mechanical Engineering Questions, Answers and Explanation 14 . The purpose of surge tank in a pipeline is to  a) smoothen the flow of water b) minimize friction loses in pipe c) prevent occurrence of hydraulic jump d) relieve pressure due to water hammer Answer d) relieve pressure due to water hammer Explanation [ Fluid Mechanics ] Surge tank is a small storage tank or reservoir required in the hydro power plants for regulating the water flow during load reduction and sudden increase in the load on the hydro generator (water flow transients in penstock) and thus reducing the pressure on the penstock. When the load on the generator is reduced suddenly (load throw-off), governor closes the turbine gates and thus create an increase in  pressure on the penstock. This may result in water " hammering effect" and may require pipe of extra ordinary strength this pressure, otherwise the penstock may burst. To avoid this positive water hammering pres...

ISRO 2014 Mechanical Engineering Questions, Answers and Explanation 18. Tension in the cable supporting a lift of weight 'W' and having an acceleration 'a' while going upward is (g is acceleration due to gravity) a) W(1+a/g) b) W(1-a/g) c) W(2+a/g) d) W(1+2a/g) Answer a) W(1+a/g) Explanation [ Engineering Mechanics ] Tension increases when the lift accelerate upwards and decreases when the lift accelerate downwards. Mass of the lift = W/g Increase in tension due to acceleration = mass of list * acceleration of lift = W/g*a Total tension = Tension due to gravity + Tension due to acceleration  = W + W/g*a = W(1+g/a) 2014. 80 . Which type of gear meshing should be employed to transmit torque to a linear force? a) Epicyclic gear b) Helical gear c) Bevel gear d) Rack and pinion Answer d) Rack and pinion Explanation [ Theory of Machines and Mechanical Vibrations ] Epicyclic gear trains have one or more axes of gears in motion. In all other gear ty...

ISRO 2012 Mechanical Engineering Questions, Answers and Explanation 8. An elevator weighing 1000 kg attains an upward velocity of 4m/sec in two seconds with uniform acceleration. The tension (in N) in supporting cable will be (g = 9.8 m/sec 2 ) a) 1204 N b) 9800 N c) 2000 N d) 11800 N Answer d) 11800 Explanation [ Engineering Mechanics ] acceleration = change in velocity/time = 4/2 2 m/s 2 Tension increases when the lift accelerate upwards and decreases when the lift accelerate downwards. So tension in supporting cable = m(g+a) = 1000 (9.8+2) = 1000 x 11.8 = 11800 N

ISRO 2011 Mechanical Engineering Questions, Answers and Explanation 9  Flow takes place at Reynolds number of 1500 in two different pipes with relative roughness of 0.001 and 0.002. The friction factor a) Will be higher for the pipe with relative roughness of 0.001 b) Will be higher for the pipe having relative roughness of 0.002 c) Will be same in both the pipes d) In the two pipes cannot be compared on the basis of data given. Answer c) Will be same in both the pipes Explanation [ Fluid Mechanics ] The friction factor f for a laminar flow (Re < 2320) in a circular pipe is given by the formula f = 64/Re. It is independent of relative roughness for the given Reynolds number 10.  A liquid compressed in cylinder has a volume of 0.04 m 3  at 50kg/cm 2  and a volume of 0.039 m 3  at 150 kg/cm 2 . The bulk modulus of elasticity of liquid is a) 400 kg/cm 2 b) 40 x 10 6  kg/cm 2 c) 40 x 10 5  kg/cm 2 d) 4000 kg/cm 2 Answe...

ISRO 2010 Mechanical Engineering Questions, Answers and Explanation 50. In simple harmonic motion the acceleration is proportional to a) Displacement b) Linear Velocity c) Angular Velocity d) Rate of change of angular velocity Answer a) Displacement Explanation [ Theory of Machines and Mechanical Vibrations ] In simple harmonic motion (SHM), some physical quantity varies sinusoidally.  Example, simple harmonic motion is a spring object system on a friction-less surface. The object is attached to one end of a spring. The other end of the spring is attached to a wall at the left. the spring force depends on the distance x , the acceleration is not constant.It is a second order linear differential equation, in which the second derivative of the dependent variable is proportional to the negative of the dependent variable.

ISRO 2009 Mechanical Engineering Questions, Answers and Explanation 2.  If the stream function of a two dimensional flow is Ψ = 3xy, then the velocity at a point (2,3) is a) 7.21 unit b) 18 unit c) 10.82 unit d) 54 unit Answer c) 10.82 unit Explanation [ Fluid Mechanics ] u = ∂ Ψ/∂ y = 3x v =-  ∂ Ψ/∂ x = -3y At (2,3), u = 3x2 = 6 unit At (2,3), v = -3x3 = -9 unit Resultant velocity = √(6 2 +(-9) 2 )= √(117)=3√(13)=10.81 unit

ISRO 2016 Mechanical Engineering Questions, Answers and Explanation 54. Which of the following order of crystal structure will match with metals Iron - Copper - Zinc in that order? a) BCC - FCC - HCP b) FCC - BCC - HCP c) HCP - FCC - BCC d) BCC - FCC - HCP Answer d) BCC - FCC - HCP Explanation [ Material Science ] BCC - Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Barium (Ba), Vanadium (V), Chromium (Cr), Iron (Fe). The bcc arrangement does not allow the atoms to pack together as closely as the fcc or hcp arrangements. Metals which have a bcc structure are usually harder and less malleable than close-packed metals such as gold. When the metal is deformed, the planes of atoms must slip over each other, and this is more difficult in the bcc structure.  FCC - Aluminium (Al), Copper(Cu), Gold (Au), Iridium (Ir), Lead(Pb), Nickel (Ni), Platinum (Pt), Silver (Ag). HCP - Beryllium(Be), Cadmium (Cd), Magnesium (Mg), Titanium (Ti), Zinc (Zn), Zirconium (Zr)

ISRO Mechanical Engineering Material Science Questions, Answers and Explanation Crystal Structure 2016.54.  Which of the following order of crystal structure will match with metals Iron - Copper - Zinc in that order? a) BCC - FCC - HCP b) FCC - BCC - HCP c) HCP - FCC - BCC d) BCC - FCC - HCP Answer d) BCC - FCC - HCP 2018.8.  Which of the following order of crystal structure will match with metals Iron-Nickel-Titanium in that order at room temperature a) BCC - HCP - FCC b) FCC - BCC - HCP c) HCP - FCC - BCC d) BCC - FCC - HCP Answer d) BCC - FCC - HCP Explanation BCC - Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Barium (Ba), Vanadium (V), Chromium (Cr), Iron (Fe). The bcc arrangement does not allow the atoms to pack together as closely as the fcc or hcp arrangements. Metals which have a bcc structure are usually harder and less malleable than close-packed metals such as gold. When the metal is deformed, the planes of atoms must slip o...