Answer:
m₂ = 3kg
Explanation:
The question wasn't clear about what direction the initial velocity of the second cart was, so I'll assume it was going left at 2.0m/s.
Anyway, this is a conservation of momentum problem. The equation you need to use is the one written in blue. They want you to solve for the mass of the second cart, so do some algebra and rearrange that blue equation in term of m₂.
Now that you have the equation for m₂, plug in all the values given from the question and you'll get 3kg.
