A ball bearing rolls along a smooth horizontal tabletop and crashes head-on into a second, stationary ball bearing of half its mass. If both ball bearings roll in the x-direction only (either positive or negative) and the initially stationary ball is observed to have a velocity of +2.4 m/s after the collision, what was the initial speed of the first ball bearing? Assume the collision is elastic.

▸

More information is required

▸

7.2 m/s

▸

3.6 m/s

▸

1.8 m/s