NHPC JE'21 ME: Daily Practices Quiz. 25-Nov-2021

Quiz: Mechanical Engineering
Exam: NHPC JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 6 Minutes

Q1. A closed thermodynamic system is one in which
(a) there is no energy or mass transfer across the boundary
(b) there is no mass transfer, but energy transfer exists
(c) there is no energy transfer, but mass transfer exists
(d) both energy and mass transfer take place across the boundary, but the mass transfer is controlled by valves

Q2. Fatigue life of a material can be improved
(a) By electroplating
(b) By polishing
(c) By coating
(d) By shot Peening

Q3. A key which is square in shape is used to transmit torque (T) from the shaft to the hub. The relationship between induced compressive stress (σc) and shear stress (τ) is
(a) σ=τ
(b) σ=2τ
(c) σ=τ/2
(d) σ=τ/4

Q4. The leakage in a refrigeration system using ammonia is detected by
(a) Halide torch
(b) Sulphur sticks
(c) Soap solution
(d) Hot water

Q5. If a beam is supported on more than two supports, is called a:
(a) Continuous beam
(b) Simply supported beam
(c) Encastered beam
(d) build in beam

Q6. The composition of German silver is
(a) 12.5% silver
(b) 5% silver
(c) 1% silver
(d) None of the above

Solutions

S1. Ans.(b)
Sol. A closed system consists of fixed amount of mass and no mass can cross its boundary but energy in the form of heat and work can cross the boundary.

S2. Ans. (d)
Sol. Shot peening is a cold working process which is used to finish machine components to improve fatigue and stress corrosion. Without changing material design shot peening can be done.

S3. Ans. (b)
Sol. Let torque transmitted by shaft is T, a is the side of the key and l be the length of the key.
Then tangential force acting on the key is
F=2T/d
Shear stress in square key

τ=(shear force)/(shear area of the key)=(2T/d)/al=2T/dal
Compressive stress in square key
σ=(compressive force)/(comressive area)=(2T/d)/(a/2 l)=4T/dal
Hence,
σ=2τ

S4. Ans. (b)
Sol. The leakage in a refrigeration system using ammonia is detected by Sulphur sticks.

S5. Ans.(a)
Sol. if a beam is supported on more than two supports is called continuous beam.

S6. Ans. (d)
Sol. There is no contamination of silver in German silver we can call it German silver just because it is appearing as silver.
German silver contains 60% cu, 20% Ni, and 20% Zn.