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 is the velocity of the first ball after the collision? Assume the collision is elastic.

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−2.4 m/s

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+2.4 m/s

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−1.2 m/s

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+1.2 m/s

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−0.6 m/s

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+0.6 m/s