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# UPPSC Lec’21 ME: Daily Practices Quiz. 26-Oct-2021

Quiz: Mechanical Engineering
Exam: UPPSC Lecturer
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 8 Minutes

Q1. The damping ratio in case of critical damping is…………………….
(a) Equal to one
(b) Equal to zero
(c) Less than one
(d) Greater than one

Q2. A differential gear in an automobile is a
(a) simple gear train
(b) epicyclic gear train
(c) compound gear train
(d) speed reducer

Q3. In a triangular notch there is an error of 8% in observing the head. The error in the computed discharge is
(a) 10%
(b) 6%
(c) 12%
(d) 20%

Q4. The maximum velocity of a one-dimensional, incompressible flow between two fixed parallel plates is 6 m/s. The mean velocity (in m/s) of the flow is
(a) 3.33
(b) 2
(c) 1.33
(d) 2.33

Q5. The boundary layer separates from the surface when
(a) du/dy=0 and dp/dx=0
(b) du/dy=0 and dp/dx>0
(c) du/dy<0 and dp/dx>0
(d) du/dy=0 and dp/dx<0

Q6. Viscosity of water in comparison to mercury is
(a) Lesser
(b) Higher
(c) Equal
(d) Unpredictable

### Solutions

S1. Ans. (a)
Sol Damping factor is the ratio of damping coefficient (c) and critical damping coefficient (Cc)
Damping factor, ς=C/c_c
ς = 1, critically damped system
ς > 1, over damped system

S2. Ans. (b)
Sol. differential gear mechanism works on the principle of epicycle gear train.

When the car is on a straight road, the ring gear, differential cage, differential pinion gear and two differential side gears all tum as a unit. The two differential pinion gears do not rotate on the pinion shaft; therefore, they exert equal force on the two differential side gears. As a result, the side gears turn at same speed as the ring gear, which causes both the drive wheels to turn at same speed. However, when the car begins to round a curve, the differential pinion gears rotate on the pinion shaft. This permits the outer wheel to turn faster than the inner wheel.

S3. Ans (d)
Sol. For triangular notch,
Q=〖(H)〗^(5/2)
So, Error in discharge dQ/Q=5/2 dH/H
Given, error in observing head= 8%
Hence, Error in discharge dQ/Q=5/2×8=20%

S4. Ans (a)
Sol. We know that following expression is valid for the mean velocity in one-dimensional, incompressible flow between two fixed parallel plates.
U_mean=〖2/3 U〗_max
U_mean=2/3×6=3 m/s

S5. Ans (b)
Sol. Boundary layer Separation

If +ve pressure gradient exists, fluid particles have to move up the pressure hill, so velocity decreases. If the velocity reduction is more, then the flow becomes reverse. This +ve pressure gradient is called adverse pressure gradient.

No Separation About to separate Detached flow
(Attached flow) (Separation point (τ=0) )

S6. Ans. (a)
Sol. Viscosity of water in comparison to mercury is lesser

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