A 225 kg red bumper car is moving at 3.0 m/s. It hits a stationary 180 kg blue bumper car. The red and blue bumper cars combine and hit a stationary green bumper car of mass 150 kg. The red, blue, and green bumper cars all combine.

Momentum is conserved in both collisions, so the final combined cars have the same total momentum as the moving red car: 225 kg × 3.0 m/s = 675 kg·m/s. Their combined mass is 225 + 180 + 150 = 555 kg. The final speed is 675 ÷ 555 ≈ 1.2 m/s, so the correct choice is 1.2 m/s.

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