Let's look at our Problem guys! A red rover that was 120kg was travelling at 3m/s. A blue rover was a 119 kg and was travelling at 3.5 m/s. They both collided and then the blue rover sped by an extra 3 m/s. What would be the final velocity of the red rover.
We would first multiply the mass and the initial velocity for both the red and blue rovers, you should add your answers which would be 776.5 kg m/s .We will then multiply the final velocity and mass for the blue cart. You should have 773.5 kg m/s. then subtract 773.5 from 776.5. We can subtract because they are the same unit.
now we are left with 3kg m/s= 120 Vfa. We will divide 3 by 120/ leaving us with our answer of Vf= .025 m/s.