Aptitude Test Problems in Physics Science for Everyone by S Krotov ( PDFDrive.com )

1. Mechanics 27

Find all possible values of the coefficient

of friction p. between the rod and the wall.

1.49*. A massive disc rotates about a verti-

cal axis at an angular velocity 5-2. A smaller

disc of mass m and radius r, whose axis is

strictly vertical, is lowered on the first

disc (Fig. 22). The distance between the axes

of the discs is d (d > r), and the coeffi-

cient of friction between them is

Determine the steady-state angular veloc-

ity 0) of the smaller disc. What moment of

force must be applied to the axis of the

larger disc to maintain its velocity of rota-

tion constant? The radius of the larger disc

is R > d r. The friction at the axes of

the discs should be neglected.

Fig. 22

Fig. 23

1.50. Two rigidly connected homogeneous

rods of the same length and mass m 1 and

m 2 respectively form an angle n/2 and rest
on a rough horizontal surface (Fig. 23).
The system is uniformly pulled with the
help of a string fixed to the vertex of the
angle and parallel to the surface.