Mechanical Operations


In ball mill operation, the feed size (Df in meters) and the ball diameter (Db in metres) are related as ( where, K = grindability constant (varying from 0.9 to 1.4 in increasing order of hard ness))

A. `D_b^2 = K.D_f`
B. `D_b = K.D_f`
C. `D_b^3 = K.D_f`
D. `D_b^2 = K.D_f^2`


Pick out the correct statement.

A. Plastic chips are called non-cohesive solids
B. Kick's crushing law is, P/m = K . ln`((overline(D)_(sa))/(overline(D)_(sb)))`
C. Communition is a generic term for size enlargement operation
D. Energy required in kwh per ton of product, such that 80% of it passes through a 200 mesh screen, is called 'Work index'.


The sphericity of a solid particle of cubical shape is

A. `pi`
B. (`pi`/`6)^(1//3)`
C. (`pi`/`6)^(1//2)`
D. `pi`/3


Velocity of a small particle of diameter 'Dp' at a distance 'r' from the rotational axis of a cyclone rotating at an angular speed `omega` is given by (the other symbols are as per standard notation)

A. `( D_p/18 . (Ps - p)/(mu)) omega ^2 r`
B. `( D_p^2/18 . (Ps - p)/(mu)) omega r^2`
C. `( D_p/18 . (Ps - p)/(mu)) omega ^2 r^2`
D. `( D_p^2/18 . (Ps - p)/(mu)) omega^2 r`


The specific surface of spherical particles is given by (where D and`rho` are diameter and density of particle).

A. `(6)/(D.rho)`
B. `(2)/(D.rho)`
C. `(4)/(D.rho)`
D. `(12)/(D.rho)`