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,Underdampad system
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