Solutions 151Thus, for an arbitrary relation between the
angles a and 0, the rod is in equilibrium if
(^1 1 2)
3 I
(^) I
tan a tan 0
1.49*. Let us analyze the motion of the smaller
disc immediately after it comes in contact with the
larger disc.
We choose two equal small regions of the small-
er dim lying on the same diameter symmetrically
about the centre 0' of this disc. In Fig. 156,
Ffrt
0
Fig. 56
points A 1 and A 2 are the centres of mass of these re-
gions. At the moment of contact (when the smaller
disc is still at rest), the velocities v 1 and v 2 of the
points of the larger disc which are in contact with
points Al and A2 of the smaller disc are directed as
shown in Fig. 156 (v 1 = 52•0.4 1 and v 2 = Q • 0A 2 ).
The forces of friction Fri and Ftr2 exerted by the
larger disc on the centres of mass A 1 and A, of
the selected regions of the smaller disc will obvi-
ously be directed at the moment of contact along
the velocities v 1 and v2 (Ftri = Ffr2)• Since the arm
ll of the force Ffri about the axis of the smaller
disc is smaller than the arm 12 of the force Ffr2
(see Fig. 156), the total torque of the couple Ffri