UPSSSC JE'21 ME: Daily Practices Quiz. 15-Sep-2021

Quiz: Mechanical Engineering
Exam: UPSSSC
Topic: Fluid Mechanics

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 8 Minutes
Q1. A bucket of water hangs with a spring balance. If an iron piece is suspended into water from another support without touching the sides of the bucket, the spring balance will show
(a) an increased reading
(b) a decreased reading
(c) no change in reading
(d) increased or decreased reading depending on the depth of immersion

Q2. The centre of buoyancy is
(a) Centre of gravity of the body
(b) point of intersection of the buoyant force and the gravitational force
(c) point of intersection of the buoyant force and the centre line of the body
(d) centre of the volume of the displaced fluid

Q3. For an irrotational motion
(a) The fluid element does not undergo any shear
(b) The fluid particles do not undergo a circular motion
(c) The circulation around any path is zero
(d) The viscosity may not be zero

Q4. The device which is used for measuring wind speed is
(a) Venturimeter
(b) Orifice meter
(c) Anemometer
(d) None of these

Q5. Why are surge tanks used in pipeline?
(a) To reduce frictional loss in pipe
(b) To ensure uniform flow in pipe
(c) To relieve the pressure due to water hammer
(d) To reduce cavitation

Q6. Air is flowing over a flat plate with a free steam velocity of 24 m/s, and its kinematic viscosity is 72×10^(-6) If a particular point, the Reynolds number is 30000, its location from the leading edge is.
(a) 0.05 m
(b) 0.07 m
(c) 0.08 m
(d) 0.09 m

Solutions
S1. Ans.(c)
Sol. Since the water of the bucket will exert force of buoyancy equal to the volume displaced by the iron block. Hence equal and opposite force will be exerted by iron block on water, hence the reading of the spring balance will increase.

S2. Ans.(d)
Sol. The centre of buoyancy is the centre of the volume of the displaced fluid.

S3. Ans.(c)
Sol.
For irrotational motion, the circulation around any path is zero because circulation is the product of vorticity and area. Vorticity is twice of rotation. Hence, for an irrotational motion, vorticity is zero and hence circulation is zero.

S4. Ans.(c)
Sol.
Anemometer: It is a device for measuring wind speed, and it is a common weather station instrument.
Orifice plate: It is a device used for measuring the volumetric flow. It uses the Bernoulli’s principle.

S5. Ans.(c)
Sol.
Surge tank is an open reservoir provided in between penstock to
(i) absorb the pressure wave due to sudden blockage of flow in the turbine which will reduce water pressured hammer problem
(ii) to serve for emergency supply and to maintain constant head at inlet of turbine

S6. Ans.(d)
Sol.
Re=ux/ϑ
x=(30000×72×10^(-6))/24=0.09 m=9 cm