Quiz: Mechanical Engineering 17 July 2020

Quiz: Mechanical Engineering
Exam: ISRO (TECHNICAL ASST.)
Topic: Miscellaneous

Each question carries 4 mark.
Negative marking: 1 mark
Time: 15 Minute

Q1. Which one does not form a part of the gating system for a casting:
(a) Pouring basin
(b) Sprue
(c) Choke
(d) Pattern

Q2. Weld spatter defect in welding is generally the result of
(a) Using tool with high welding current
(b) Using tool with low welding current
(c) Low voltage
(d) High voltage

Q3. A good machinability rating would indicate:
(a) long tool life, high power requirement and less machining time
(b) long tool life, low power requirement and a good surface finish
(c) short tool life and a good surface finish
(d) long tool life, high power requirement and a good surface finish

Q4. Which one of the following devices produces incremental motion through equal pulses?
(a) AC servomotor
(b) DC servomotor
(c) Stepper motor
(d) Series motor

Q5. What is the preferred order of sequence for the following drives from high speed to low speed?
(a) Rack and pinion, spur gears, worm and worm wheel
(b) worm and worm wheel, spur gears, rack and pinion
(c) Worm and worm wheel, rack and pinion, spur gears
(d) Spur gears, worm and worm wheel, rack and pinion

Q6. If the angle of repose is 30°, the maximum efficiency of screw for motion up the inclined plane is:
(a) 50%
(b) 33.3%
(c) 75%
(d) None of these

Q7. The strain energy of the spring when it is subjected to the greatest load which the spring can carry without suffering permanent distortion is known as:
(a) Limiting stress
(b) Proof stress
(c) Proof resilience
(d) Proof load stress

Q8. A lead ball with a certain velocity is made to strike a wall, it falls down, but rubber ball of same mass and the same velocity strikes the same wall, it rebounds. Select the correct reason from the following:
(a) Both the balls undergo an equal change in momentum
(b) the change in momentum suffered by rubber ball is more than the lead ball
(c) the change in momentum suffered by rubber ball is less than the lead ball
(d) None of these

Q9. When the speed of a centrifugal pump is tripled, the power required to drive the pump will:
(a) Triple
(b) becomes 9 times
(c) becomes 27 times
(d) remains the same

Q10. Anything that generates entropy always:
(a) increases enthalpy
(b) decreases pressure
(c) decreases energy
(d) lowers chemical reaction

Solutions

S1. Ans (d)
Sol. Gating system has the following parts for a casting:
1. Pouring basin
2. Sprue
3. Choke

S2. Ans (a)
Sol. Weld spatter is usually seen when the welding voltage is too low or the amperage is too high for a given wire and gas combination.

S3. Ans (b)
Sol. Machinability index designates the degree of difficulty or ease with which a particular material can be machined. A good machinability rating or index represents long tool life, low power requirement and a good surface finish.

S4. Ans (c)
Sol. Stepper motors are DC motors that move in discrete steps. They have multiple coils that are organized in groups called phases. By energizing each phase in sequence, the motor will rotate, one step at a time.

S5. Ans (c)
Sol. The preferred order of sequence of the drives from high to low speed:
1. Worm and worm wheel
2. Rack and pinion
3. Spur gears

S6. Ans (b)
Sol. Given,
Angle of repose (θ) = 30°
Maximum efficiency of screw for motion up the inclined plane = (1-sinθ)/(1+sinθ)
= (1-sin30)/(1+sin30)
= 33.3%

S7. Ans (c)
Sol. Proof resilience is defined as the maximum energy that can be absorbed up to the elastic limit, without creating a permanent distortion.

S8. Ans (b)
Sol. As both lead and rubber balls have same mass and velocity, if rubber ball rebounds then there is more change in momentum of it than that of lead ball.

S9. Ans (c)
Sol. We know that
Power(P) ∝ Speed(N)^3
So, pump power requirement becomes 27 times the previous value.

S10. Ans (b)
Sol. If there is an entropy generation then definitely, there is a presence of temperature or pressure gradient. It means if pressure or temperature decreases then entropy generation takes place due to irreversibility.

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