NHPC JE'21 ME: Daily Practices Quiz. 16-Nov-2021

Quiz: Mechanical Engineering
Exam: NHPC JE
Topic: Miscellaneous

Each question carries 1 mark
Negative marking: 1/4 mark
Time: 8 Minutes

Q1. If the Euler load for a column is 100 kN and crushing load is 120 kN, then the Rankine load will approximately be:
(a) 120
(b) 60
(c) 90
(d) 54

Q2. The damping ratio in case of over damping is…………………….
(a) Equal to one
(b) Equal to zero
(c) Less than one
(d) Greater than one

Q3. A differential gear in an automobile is a
(a) simple gear train
(b) epicyclic gear train
(c) compound gear train
(d) speed reducer

Q4. The thrust approaches to ……… when the propulsive efficiency of a turbo-jet aircraft approaches 100%
(a) Maximum
(b) 50% of the maximum
(c) 25% of the maximum
(d) Zero

Q5. A plane wall of thickness 25 cm with an area of 2 m² and thermal conductivity of 0.5 W/m-K is provided to a furnace. If a temperature difference of 50°C is imposed across it, what is the heat flow?
(a) 200 W
(b) 140 W
(c) 160 W
(d) 180 W

Q6. In a Mohr’s circle of σ-τ plane (σ = normal stress, τ = shear stress), the vertical diameter represents
(a) Maximum shear stress
(b) Maximum normal stress
(c) Principal stress
(d) Minimum normal stress

Solutions
S1. Ans. (d)
Sol. Pe= 100 KN
Pcr = 120 KN
Rankine load = ?
1/P=1/Pe+1/Pc
1/P=1/100+1/120
P= 54.545 KN

S2. Ans. (d)
Sol Damping factor is the ratio of damping coefficient (c) and critical damping coefficient (Cc)
Damping factor, ς=C/c_c
ς<1,Underdampad system
ς = 1, critically damped system
ς > 1, over damped system

S3. Ans. (b)
Sol. differential gear mechanism works on the principle of epicycle gear train.

When the car is on a straight road, the ring gear, differential cage, differential pinion gear and two differential side gears all tum as a unit. The two differential pinion gears do not rotate on the pinion shaft; therefore, they exert equal force on the two differential side gears. As a result, the side gears turn at same speed as the ring gear, which causes both the drive wheels to turn at same speed. However, when the car begins to round a curve, the differential pinion gears rotate on the pinion shaft. This permits the outer wheel to turn faster than the inner wheel.

S4. Ans. (d)
Sol.
Propulsive efficiency is maximum when jet velocity (C_j )= forward velocity of aircraft (C_a)
Now thrust power = (C_j-C_a ) C_a=0
i.e., at maximum efficiency thrust power is zero.

S5. Ans. (a)
Sol.
Q=kA(T_1-T_2 )/l
=(0.5×2×50)/0.25=200 W

S6. Ans. (a)
Sol. In Mohr’s circle vertical axis represent shear stress & Horizontal axis represent normal stress so the vertical diameter of circle represents maximum shear stress.