NHPC JE’21 ME: Daily Practices Quiz. 08-Oct-2021

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NHPC-JE’21 ME: Daily Practices Quiz

NHPC-JE’21 ME: Daily Practices Quiz 08-Oct-2021

Quiz: Mechanical Engineering
Exam: NHPC JE
Topic: Machine Design

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

Q1. S-N curve represents the:
(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. Notch sensitivity varies between:
(a) 0–10
(b) 0.1 – 100
(c) 1 – 100
(d) 0–1

Q3. The failure of a material under varying load, after a number of cycles of such load, is known as
(a) Ductile failure
(b) Brittle failure
(c) Impact failure
(d) Fatigue failure

Q4. The factor of safety provided for the cotter is less than that for the spigot and socket end because
1. There is stress concentration in the cotter
2. There is no stress concentration in the cotter
3. The cotter is not as weaker as the spigot and socket end
4. The cotter has been made from materials different from that of the spigot and socket end
Which of the above statements are correct?
(a) 1 and 3 only
(b) 1 and 4 only
(c) 2 and 3 only
(d) 2 and 4 only

Q5. An engine running at 150 r.p.m. drives a shaft with belt arrangement. If diameter of engine pulley is 55 cm and shaft pulley 33 cm, find the speed of shaft: –
(a) 100 rpm
(b) 150 rpm
(c) 200 rpm
(d) 250 rpm

Q6. The product of the tangential force acting on the shaft and its distance from the axis of the shaft (i.e., radius of shaft) is known as:
(a) Bending moment
(b) Twisting moment
(c) Torsional rigidity
(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).

S-N curve—S-N curve, a graphical representation of a cyclic loading, is a plot of fatigue strength versus the number of cycles the material gas through before it fails.

S2. Ans(d)
Sol. Notch sensitivity is defined as the ratio of increase of actual stress over nominal stress in fatigue to the increase stress over nominal stress in static loading.
q=(K_f-1)/(K_t-1)
where,
K_f = actual (or) fatigue stress concentration factor.
K_t = theoretical (or) static stress concentration factor.

S3. Ans(d)
Sol. The failure of a material under varying load, after a number of cycles of such load, is known as fatigue failure, material to be fracture by means brittle cracking under repeated cyclic stresses.

S4. Ans(c)
Sol. Spigot is the male part of the joint, it has a rectangular slot for passing the cotter through it. Spigot has a collar which rests against the socket end. Socket is the female part of the joint, it also has a rectangular slot for passing the cotter through it. Cotter is a wedge-shaped piece of metal which actually connects two part which re non rotating. The factor of safety for cotter is less than the spigot and socket because, there is no stress concentration in the cotter and resulting high strength than spigot and socket end.

S5. Ans(d)
Sol. given that-
N_1=150 rpm
d_1=55 cm
d_2=33 cm
We know that,
N_1/N_2 =d_2/d_1
N_2/N_1 =d_1/d_2
N_2=d_1/d_2 ×N_1
N_2=55/33×150
N_2=250 rpm

S6. Ans(b)
Sol. The product of the tangential force acting on the shaft and its distance from the axis of the shaft (i.e., radius) is known as twisting moment

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