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ISRO 2006 Mechanical Questions, Answers and Explanation

ISRO 2006 Mechanical Questions, Answers and Explanation

Question Set A

1. In nodular iron, graphite is in the form of
     a) Cementite
     b) Free Carbon
     c) Flakes
     d) Spheroids

Answer
d) Spheroids

Explanation [Material Science]
Nodular cast iron is also called ductile cast iron or spheroidal graphite iron. As graphite is in the form of nodules they inhibit formation of cracks and hence more ductile.

In grey cast iron where graphite is in the form of flakes exhibit more stiffness. On extension they create concentration points and hence are less ductile.

Free carbon that is present in an elemental form is often an impurity which could be removed by smelting.

Cementite is iron carbide with 6.67% Carbon by weight.

2. Hardness of steel depends on
     a) Amount of carbon it contains
     b) The shape and distribution of of the carbides in the iron
     c) Method of fabrication
     d) Contents of alloying elements

Answer
a) Amount of carbon it contains

Explanation [Material Science]
As the carbon content in steel increases, its hardness increases.
Alloying elements other than Carbon are primarily used to reduce corrosion rate(Nickel, Copper).

2006. 3. Too high welding current in arc welding would result in
    a) Excessive splatter, under cutting along edges, irregular deposits, wasted electrodes
    b) Excessive piling up of weld metal, poor penetration, wasted electrodes
    c) Too small bead, weak weld and wasted electrodes
    d) Excessive piling up of welded metal, overlapping without penetration of edges, wasted electrodes.

Answer
a) Excessive splatter, under cutting along edges, irregular deposits, wasted electrodes

Explanation
Too low welding current - Setting the amps too low will result in a tall, narrow bead lacking in penetration. The weld will be difficult to start and the arc prone to straying towards one side of a joint in preference to the other.
Too high welding current - The bead is wide, flat and irregular, and a small undercut is formed. A deep crater has formed at the end of the weld, and the slag is difficult to remove from the edges of the weld.
Current welding current - With the amps set correctly the bead is a consistent rounded shape, and the slag is easy to remove.

2006. 4. Which of the following process would produce strongest components?
    a) Hot rolling
    b) Extrusion
    c) Cold rolling
    d) Forging

2006. 6. Which of the following has maximum hardness?
    a) Austenite
    b) Pearlite
    c) Troostite
    d) Martensite

2006. 7. The main advantage of line organization is its
     a) Effective command and control
     b) Defined responsibilities at all levels
     c) Rigid discipline in the organization
     d) All the above

2006. 8. The mathematical technique for finding the best use of limited resources in an optimum manner is known as
     a) Operations research
     b) Linear programming
     c) Network analysis
     d) Queuing theory

Answer
a) Operations research

2006. 9. Which of the following errors are generally distributed in accordance with the Gaussian distribution
     a) Controllable errors
     b) Calibration errors
     c) Avoidable errors
     d) Random errors

2006. 10. PL3/3EI is the deflection under the load P of a cantilever beam (length L, modulus of elasticity E, moment of inertia I). The strain energy due to bending is
     a) P2L3/3EI
     b) P2L6/6EI
     c) P2L6/4EI
     d) P2L6/48EI

11. A mass m attached to a light spring oscillates with a period of 2 sec. If the mass is increased by 2 kg, the period increases by 1 sec. The value of m is
     a) 1 kg
     b) 1.6 kg
     c) 2 kg
     d) 2.4 kg

Answer
b) 1.6 kg

Explanation [Theory of Machines and Mechanical Vibrations]
T = 2π √(m/k)
Case 1 - T = 2 sec, m = m kg, 2 = 2π √(m/k)
Case 2 - T = 3 sec, m = m + 2 kg, 3 = 2π √((m+2)/k)
Dividing one by another
2/3 = √ (m/(m+2))
squaring on both sides
4/9 = m/(m+2)
4m + 8 = 9m
5m = 8
m = 8/5 = 1.6 kg


2006. 12. A short column of external diameter D and internal diameter d carries an external load W. The greatest eccentricity which the load can have without producing tension on the cross section of the column is
     a) (D+d)/8
     b) (D2+d2)/8
     c) (D2+d2)/8D
     d) (D2+d2)/8d

2006. 13. If the radius of wire stretched by a load doubled, then its Young's modulus will
     a) Be doubled
     b) Be halved
     c) Become four times
     d) None of the above

2006. 14. Longitudinal stress in a thin cylinder subjected to internal pressure is
     a) Half of the hoop stress
     b) Twice the hoop stress
     c) Equal to the hoop stress
     d) One-fourth the hoop stress

2006. 15. Maximum deflection in cantilever due to pure bending moment M at its end is
     a) ML2/2EI
     b) ML2/3EI
     c) ML2/4EI
     d) ML2/6EI

2006. 16. Poisson's ration for a meterial is 0.5, then the elastic modulus for the material is
     a) 3 times its shear modulus
     b) 4 times its shear modulus
     c) Equal to its shear modulus
     d) Indeterminate

2006. 19. Which of the following relationships between the force F on a particle and the particles position x implies simple harmonic oscillation
     a) F = -7X
     b) F = -200x2
     c) F = 10x
     d) F = 5x2

2006. 21. The bending equation is written as
     a) I/M = f/y = E/R
     b) M/I = f2/y = E2/R2
     c) M/I = f/y = E/R
     d) M2/I = f2/y = E2/R

2006. 22. Hydraulic testing of boilers is done at pressures
     a) Below and above atmosphere
     b) Slightly above atmospheric pressure
     c) At half the working pressure of boiler
     d) At 1.5 to 2 times the working pressure

23. 100m of water column is equal to
     a) 1000 kN/m2
     b) 100 kN/m2
     c) 10 kN/m2
     d) 1 kN/m2

Answer
a) 1000 kN/m2

Explanation [Fluid Mechanics]
P = ρgh, ρ = 1000kg/m3, g=10m/s2, h = 100m
P = 1000x10x100 N/m2 = 1000kn/m2

2006. 24. Gantry girders are invariably designed to resist
     a) Transverse loads only
     b) Lateral loads only
     c) Transverse and lateral loads
     d) Transverse, lateral and axial load

2006. 25. If the rotating mass of a rim type flywheel is distributed on another rim type flywheel whose mean radius is half the mean radius of the former, then energy stored in the later at the same speed will be
     a) Four times the first one
     b) Same as the first one
     c) One fourth of the first one
     d) One and a half times the first one

2006. 26. A thin circular disc is rolling with a uniform linear speed, along a straight path on a plane surface. Consider the following statements in this
1. All points of the disc have the same velocity
2. The center of the disc has zero acceleration
3. The center of the disc has centrifugal acceleration
4. The point on the disc making contact with the plane surface has zero acceleration
Of these statements
     a) 1 and 4 are correct
     b) 3 and 4 are correct
     c) 3 alone is correct
     d) 2 alone is correct

2006. 27. If a number of forces act on a rigid body, each force may be replaced by an equal and parallel force acting through a fixed point, together with a couple. For the rigid body to be in equillibrium
     a) Both resultant force and couple must be zero
     b) The resultant couple on the body must be zero
     c) The resultant force at the fixed point must be zero
     d) None of the above need be zero

2006. 28. Whirling speed of a shaft coincides with the natural frequency of its
     a) Longitudinal vibration
     b) Transverse vibration
     c) Torsional vibration
     d) Coupled bending torsional vibration

2006. 29. A fixed gear having 200 teeth is in mesh with another gear having 50 teeth. The two gears are connected by an arm. The number of turns made by the smaller gear for one revolution of arm about the center of the bigger gear is
     a) 4
     b) 3
     c) 2/4
     d) 5

2006. 30. With symbols having the usual meaning, the single degree of freedom system, mx

2006. 32. Which one of the following is not a friction clutch?
     a) Disc or plate clutch
     b) Cone clutch
     c) Centrifugal clutch
     d) Jaw clutch

2006. 34. Pick up the wrong statement. A flywheel
     a) Is used to limit the inevitable fluctuation of speed during each cycle
     b) Controls the mean speed of rotation
     c) Stores up energy and gives up whenever required
     d) Regulates the speed during one cycle of a prime mover

37. A person walks up a stalled escalator in 90 seconds. When standing on the same escalator, now moving, he is carried up in 60 seconds. How much time would it take him to walk up the moving escalator.
     a) 30 sec
     b) 36 sec
     c) 45 sec
     d) 54 sec

Answer
b) 36 sec

Explanation [Engineering Mechanics]
Let the distance the person has to cover be d.
Let the velocity of the person be vm.
Let the velocity of the moving escalator be ve

When the escalator is stalled the person walks with velocity vm.
Use distance = velocity x time
d = vm x 90  ---- 1
When standing on the moving escalator the person moves with velocity ve.
d = ve x 60 ----- 2

Dividing 1 by 2 we get 1 = vm x 90 /(ve x 60)
vm = 2ve/3 ---- 3
Let the time taken for him to walk up the moving escalator be t seconds.
When walking on a moving escalator, the person moves with velocity = vm + ve
d = (vm + ve)xt
d = (2ve/3+ ve)xt, using 3
d = 5ve/3 x t
t = 3d/(5ve), but d/ve = 60 from 2
t = 3*60/5 = 36 seconds.

2006. 44. For a closed system, difference between the heat added to the system and work done by the gas, is equal to the change in
     a) Internal Energy
     b) Entropy
     c) Enthalpy
     d) Temperature

Answer
a) Internal Energy

Explanation
Closed system is one in which only energy transfer takes place. Open system is one in which both energy and mass transfer takes place.

First law of thermodynamics states that the change in internal energy equals the difference between heat supplied and work done.
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