ember s - Port 4200 is already in use

I have two ember projects: project1, project 2

project1: ember s , port 4200 is working fine. I closed the project1 terminal and again tried to start ember s inside project2, when i do that, i am getting Port 4200 is already in use.

Port 4200 is already in use.

Why am i getting this error, as other instances where already killed and how to rectify it ?