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# NHPC JE’21 ME: Daily Practices Quiz. 22-Sep-2021

## NHPC JE Recruitment 2021

National Hydroelectric Power Corporation (NHPC) has released the recruitment notification for engagement of following posts such as Senior Medical Officer, Assistant Rajbhasha Officer, Junior Engineer & Sr. Accountant posts. NHPC expects application from High Performing, Dynamic & Achievement-Oriented Professionals candidates to fill up these 173 vacancies.

### NHPC-JE’21 ME: Daily Practices Quiz

NHPC-JE’21 ME: Daily Practices Quiz 22-Sep-2021

Quiz: Mechanical Engineering
Exam: NHPC
Topic: Machine Design

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

Q1. S-N curve is the curve between
(a) Fracture toughness on y-axis and numbers of fully reversed stress cycle on x-axis
(b) Resilience on y-axis and numbers of fully reversed stress cycle on x-axis
(c) Fatigue strength on y-axis and numbers of fully reversed stress cycle on x-axis
(d) Hardness on y-axis and numbers of fully reversed stress cycle on x-axis

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. A cotter joint is used to connect two rods which are subjected to
(a) Compressive stress only
(b) Tensile as well as Compressive stress only
(c) Tensile only
(d) Shear only

Q5. The key which is used to transmits power in a taper shaft?
(a) Barth key
(b) Woodruff key
(c) Kennedy key
(d) Tangent key

Q6. Taper on the cotter and slot is provided
(a) On both the sides
(b) On one side only
(c) On none of the sides
(d) None of the above

### Solutions

S1. Ans. (c)
Sol. S-N curve represents the fatigue strength on y-axis and numbers of fully reversed stress cycle on x-axis.

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)/(compressive area)=(2T/d)/(a/2 l)=4T/dal
Hence,
σ=2τ
S4. Ans. (b)
Sol. A cotter joint is used to connect to Co-axial rods, which are subjected to either axial tensile force or axial compressive force.
Cotter Joint are used in the following cases
(i) Foundation bolt
(ii) Joint between the piston rod and the tail or pump rod.
(iii) Joint between the slide spindle and the fork of the valve mechanism
(iv) Joint between the piston and the cross head of a steam Engine

S5. Ans. (b)
Sol. The woodruff key is used to transmit power in a taper shaft.

S6. Ans. (b)
Sol. Taper on the cotter and slot is provided on one side only.

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