#### Mechanical Operations

1

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

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'.

3

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

4

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

5

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

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