Quiz: Mechanical Engineering 29 May 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. Chloro-fluoro carbons are banned due to
(a) High cost
(b) Toxicity
(c) High boiling point
(d) Preventing infrared rays to escape and allowing UV rays to earth

Q2. The ratio of thermal diffusivity to mass diffusivity is known as
(a) Schmidt number
(b) Sherwood number
(c) Lewis number
(d) Stanton number

Q3. A curve that is everywhere tangent to the instantaneous local velocity vector, is
(a) Streak line
(b) Path line
(c) Normal line
(d) Streamline

Q4. The tension in the cable supporting a lift is more when the lift is
(a) Moving downward with uniform velocity
(b) Moving upward with uniform velocity
(c) Moving upward with acceleration
(d) Moving downward with acceleration

Q5. When the temperature of a solid metal increases-
(a) strength of metal decreases but ductility increases
(b) both strength and ductility decrease
(c) both strength and ductility increase
(d) strength of metal increases but ductility decreases

Q6. Region of safety for maximum principal stress theory under bi-axial stress is shown by:
(a) Ellipse
(b) Square
(c) Pentagon
(d) Hexagon

Q7. When a nut is tightened by placing washer with it, the bolt will be subjected to following type of loads
(a) compression
(b) tension
(c) shear
(d) combined load

Q8. Which of the following is a statically indeterminate structure?
(a) Load supported on composite member
(b) Load supported on two members
(c) Load supported on three members
(d) Thermal load supported on two members

Q9. If steel is cooled in still air, the structure obtained is
(a) Pearlite
(b) Sorbite
(c) Troosite
(d) Acicular

Q10. Cutting power consumption in turning can be significantly reduced by
(a) increasing rake angle of the tool
(b) increasing the cutting angle of the tool
(c) widening the nose radius of the tool
(d) increasing the clearance angle

Solutions

S1. Ans (d)
Sol. Chloro-fluoro carbon has been banned due to its high ozone depletion potential as it allows UV rays to come on the earth and high global warming potential as it absorbs infrared rays coming from sun.

S2. Ans (c)
Sol. Lewis number is defined as the ratio of thermal diffusivity to mass diffusivity. It is used to characterize fluid flows where there is simultaneous heat and mass transfer.

S3. Ans (d)
Sol. A curve that is everywhere tangent to the instantaneous local velocity vector, is called stream line. The equation of streamline is,
(dx/u=dy/v=dz/w)

S4. Ans (c)
Sol. Tension in the cable will be more when the lift is moving upward with constant acceleration as compared to when the lift is moving downward.
For upward acceleration, tension (T) in the cable;
T=Mg+Ma
For downward acceleration, tension (T) in the cable;
T=Mg-Ma

S5. Ans (a)
Sol. When the temperature of a solid metal increases then strength of the metal decreases and ductility increases due to breaking in inter-molecular bonds in the metal.

S6. Ans (b)
Sol. Region of safety for maximum principal stress theory under bi-axial stress is shown by a square. Maximum principal stress theory is used for the design of brittle material.

S7. Ans (b)
Sol. When a nut with washer is tightened on a bolt then the nut is subjected to compressive stress and the bolt is subjected to tensile stress.

S8. Ans (c)
Sol. In statics and structural mechanics, a structure is statically indeterminate when the static equilibrium equations are insufficient for determining the internal forces and reactions on that structure. When load is applied on three members simultaneously then it is called statically indeterminate.

S9. Ans (b)
Sol. If steel is cooled in still air, the structure obtained is Sorbite. It is formed by rapid cooling of steel heated to above 400˚C. It is softer and more ductile than Troosite.

S10. Ans (a)
Sol. We know, according to Merchant’s theory,
∅+β-α=π/2
If α↑then ∅↑ and shear area decreases which causes to decrease in cutting force and consequently cutting power.

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