# Mechanical Operations Questions and Answers – Crusher Operations

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This set of Mechanical Operations Multiple Choice Questions & Answers (MCQs) focuses on “Crusher Operations”.

1. Which of the following doesn’t work on the principle of flotation?
a) Fagergreen machine
b) D-R machine
c) Agitair machine
d) Norton separator

Explanation: The Norton separator works and based on the principle of the electromagnetic induction of charged particles, while all other three are based on flotation.

2. In a DR machine, the stator and rotor works as a _____
a) Bending action
b) Shearing action
c) Tangential action
d) Trawling action

Explanation: The shearing action of the rotor and the stator breaks the air into minute bubble, this randomly distributes air between all the feed.

3. For a DR flotation, the feed enters from ____
a) Bottom
b) Top
c) Middle
d) Batch type

Explanation: In DR flotation machine, the pulp enters the top of recirculation well, while low pressure air enters through the air passage.
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4. What eliminates the formation of granular solids?
a) Stabilizer
b) Modifier
c) Forth agent
d) Collector

Explanation: Stabilizer eliminates the formation of granular materials in the corners or at the bottom of the cell, so that total cell volume is utilized.

5. For electro flotation, gas bubbles are generated ____
a) Magnetically
b) Electrolytically
c) Manually
d) Electrically

Explanation: Gas bubble are generated electrolytically within the suspension, and attach themselves to the suspended particles.

6. The below equation represents ____

F = 3πμdu

a) Navier stoke
b) Reynold’s
c) McCabe
d) Newton’s

Explanation: In 1851, Stokes who solved the hydrodynamic equations of motion, the Navier–Stokes equation as given above, where F is the Drag force.

7. The drag force coefficient CD is ____
a) 2R’/pu2
b) 2R’/pu3
c) 2R’/pu
d) R’/pu0.5

Explanation: The drag force coefficient is defined as the ratio of R’ to the half the product of the density and the square of velocity.

8. If a particle is moving in a fluid which is in laminar flow, the drag coefficient is _____
a) To that in turbulent flow
b) To that in still fluid
c) To that in tank
d) To that in viscous

Explanation: In a fluid which is in laminar flow, the drag coefficient is equal to that in still fluid, provided at the local relative velocity.

9. Electrode fouling can be prevented by ________
a) Reversing Polarity
b) Changing electrode
c) Changing dielectric
d) Nothing to change

Explanation: Electrode fouling can be prevented by periodically reversing the polarity of the electrodes, occasionally anodes may be used.

10. Flotation is faster than ___
a) Electrostatic separator
b) Purification
c) Sedimentation
d) Agitation

Explanation: Since, the flotation process is much faster than the sedimentation of fine particles, flotation can be achieved in much shorter times.

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