Quiz: Mechanical Engineering 7 Aug 2020

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

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

Q1. The pressure head loss experienced by fluid flow due to friction in a pipe increases with
(a) increasing length of pipe
(b) increasing diameter of pipe
(c) decreasing length of pipe
(d) both b and c

Q2. Which of the following statements is correct for a body in simple harmonic motion?
1. Acceleration is proportional to displacement from mean position
2. Velocity is minimum at mean position
3. Acceleration is maximum at mean position
(a) 1 and 2
(b) 2 and 3
(c) only 1
(d) only 2

Q3. The amount of heat flow in unit time by conduction
(a) Decreases with increase in area of the body
(b) Increases with increase in area of the body
(c) Increases with increase in thickness of body
(d) Decreases with increase in temperature difference between the faces of the body

Q4. If an unconstrained steel bar is heated uniformly then which of the following is correct for it?
(a) Thermal stress will be developed in it.
(b) Tensile stress will be developed in it.
(c) Compressive stress will be developed in it.
(d) No stress will be developed in it.

Q5. A rotating ceiling fan completes 800 revolutions per minute. If the tip of the blade is at a radius of 0.5 m, then the blade tip speed is (take π=22/7)
(a) 42 m/s
(b) 22 m/s
(c) 66 m/s
(d) 88 m/s

Q6. Which of the following statements are correct when related to thermodynamic system?
1. Enthalpy is a property
2. Enthalpy is path independent function
3. Enthalpy is path dependent function
(a) Only 1
(b) 1 & 2
(c) 1 & 3
(d) 2 & 3

Q7. The number of Nitrogen atoms in 56 grams of Nitrogen gas is
(a) 6.023 ×10^23
(b) 12.023 ×10^23
(c) 24.092 ×10^23
(d) 6.023 ×10^27

Q8. If feed per revolution is 2 mm and lathe spindle is rotating with 600 rpm then find out the time taken to machine 400 mm length workpiece
(a) 0.33 sec
(b) 20 sec
(c) 2 min
(d) 1.33 sec

Q9. Which of the following milling processes is also called climb up milling?
(a) Up-milling
(b) Down-milling
(c) Face-milling
(d) End-milling

Q10. Which of the following thread is used for bench vices?
(a) Acme
(b) Square
(c) Buttress
(d) Trapezoidal

Solutions

S1. Ans (a)
Sol. We know that pressure head loss in a pipe is given by Darcy-Weisbach’s equation.
h=(fLV^2)/(d.2g)
Here, h increases with decreasing diameter and increasing length of the pipe.

S2. Ans (c)
Sol. In simple harmonic motion, acceleration of a particle is proportional to the displacement from the mean position.
i.e. Acceleration ∝-(Displacement)
Acceleration is minimum at the mean position and maximum at the end positions.

S3. Ans (b)
Sol. We know that Fourier’s law of conduction for heat flow rate is given by
Q=-kA.dT/dx
Q increases with increasing area and temperature difference and Q decreases with increasing thickness of the wall along the heat flow.

S4. Ans (d)
Sol. Stress is defined as internal resistance invoked by a body to the external forces. If there is no external force on the body then there is no stress in it. Hence, in an unconstrained steel bar, there is no stress due to heating.

S5. Ans (a)
Sol. Blade tip speed for a rotor is given by
V=rω …………(1)
Given,
N= 800 rpm then ω=2πN/60=(2×22×800)/(60×7)
From equation (1)
V=0.5×(2×22×800)/(60×7)
V=41.9 or 42 m/s

S6. Ans (b)
Sol. Enthalpy is a property of a thermodynamic system. So, it is path-independent function.

S7. Ans (c)
Sol. According to Avogadro’s Law,
1 mole (or 28 grams) of Nitrogen gas contains 6.023 ×10^23 molecules, so, 56 grams of Nitrogen gas contains 12.046×10^23 molecules.
1 molecule (or 28 grams) of Nitrogen gas has 2 mole-atoms, hence 56 grams (or 2 molecules) of Nitrogen gas has four mole-atoms or 24.092 ×10^23 atoms.

S8. Ans.(b)
Sol.Given,
N=600 rpm
L=400 mm
Feed per rev= 2 mm
Time taken to machine the component=L/fN=400/2X600
=0.33 minute or 20 sec

S9. Ans (a)
Sol. Up-milling is a milling process in which cutter moves in the opposite direction of work-piece motion. It is also called conventional milling process because of its cutter motion opposite to the work-piece.

S10. Ans (c)
Sol. The buttress thread form, also known as the breech-lock thread form, refers to two different thread profiles. Buttress threads are used for one side motion transmission only i.e. in bench vices etc.

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