Quiz:Mechanical Engineering 27 April 2020

Quiz: Mechanical Engineering
Exam: UPSSSC JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 10 Minutes

Q1. The rise or fall of head ‘h’ in a capillary tube of diameter ‘d’ and liquid surface tension σ and specific weight w is equal to
(a) 4σ/wd
(b) 4dσ/w
(c) 4wd/σ
(d) 4wσ/d

Q2. As per law of fluid friction for steady streamline flow, the frictional resistance;
(a) Varies proportionally to pressure
(b) varies in inverse proportion to pressure
(c) does not depend on pressure
(d) first increase then decreases

Q3. Meta-centric height is the distance between-
(a) Meta Center and water surface
(b) Meta Center and Center of buoyancy
(c) Meta Center and Center of gravity
(d) meta Center and centroid

Q4. An empty bucket of negligible weight is inverted, forced down and submerged completely slightly below the water surface. Select the outcome from below that would be an incorrect outcome.
(a) The water enters the bucket up to some distance above the rim
(b) pressure of air in the bucket rises above atmospheric pressure
(c) A force needs to be exerted downward on it to keep it submerged
(d) if released, the bucket will sink

Q5. A thermodynamic system refers to
(a) any defined region in space
(b) a specified mass in fluid flow
(c) a specified region of constant volume
(d) a prescribed and identifiable quantity of matter

Q6. In highly rarefied gases, the concept of this loses validity
(a) thermodynamic equilibrium
(b) continuum
(c) stability
(d) macroscopic point of view

Q7. Which one of the following sequences indicates the correct order for flue gas flow in
the steam power plant layout?
(a) super-heater, economizer, air preheater
(b) economizer, air preheater, super-heater
(c) air preheater, economizer, super-heater
(d) economizer, super-heater, air preheater

Q8. In centrifugal compressor terminology, vane less space refers to the space between
(a) The inlet and blade inlet edge
(b) Blades in the impeller
(c) Diffuser exit and volute casing
(d) Impeller tip and diffuser inlet edge

Q9. Where does mixing of fuel and air take place in case of diesel engine?
(a) Injection pump
(b) Injector
(c) Engine cylinder
(d) Inlet manifold

Q10. Detonation in the SI engine becomes severe during
(a) Low load and high speed
(b) High load and high speed
(c) Low load and low speed
(d) High load and low speed

Solutions

S1. Ans(a)
Sol. Capillary rise or fall
h = 4σcosθ/ρgd
But w(weight density) = ρg,
and cosθ for water and glass = 1
So,(h=4σ/wd)

S2. Ans(c)
Sol. The frictional resistance as per law of fluid friction for steady streamline flow, depends on viscosity which causes the viscous forces between two adjacent layers. There is no relation between pressure and frictional resistance.

S3. Ans(c)
Sol.

S4. Ans(d)
Sol. The bucket will not sink after releasing the force which was required to submerged because the bucket have negligible weight.

S5. Ans(d)
Sol.

S6. Ans(b)
Sol. Continuum: In this approach we consider systems to be a continuous form of matter. It means that we do not consider the gaps/spaces between the atoms or molecules that are actually present. Instead, we consider a uniform distribution of matter with no spaces or gaps.
But in rarefied gas, gaps will be created among atoms and molecules, so this approach becomes invalid.

S7. Ans(a)
Sol. The correct order is super-heater, economizer, air preheater.

S8. Ans(d)
Sol.

S9. Ans(c)
Sol. Diesel is directly injected in cylinder where it gets mixed with air.

S10. Ans(d)
Sol. Detonation in SI engine will become severe at high load and low speed because at
higher loads, the temperature of cylinder and combustion chamber walls will be higher
and hence temperature of the end charge will be more which increases knocking
tendency in SI engine.
And at lower engine speed, longer will be the absolute time for the flame to traverse the
cylinder which increases the time available for pre flame reactions hence the tendency to
knock increases.