Solution:
The mass of the ball bearing is given as $\mathrm{m}$
Before the collision, Total Kinetic Energy of the system will be
$=1 / 2 m v^{2}+0=1 / 2 m v^{2}$
After the collision, Total Kinetic Energy of the system is
Case I, $E_{1}=(1 / 2)(2 m)(v / 2)^{2}=1 / 4 \mathrm{mv}^{2}$
Case II, $E_{2}=(1 / 2) \mathrm{mv}^{2}$
Case III, $\mathrm{E}_{3}=(1 / 2)(3 \mathrm{~m})(\mathrm{v} / 3)^{2}=3 \mathrm{mv}^{2} / 18=1 / 6 \mathrm{mv}^{2}$
Thus, case II is the only possibility since K.E. is conserved in this case.
Thus,
is only possible since KE of the system is conserved