Coop jobs are full time jobs. They generally run from January to June or from July though December. You are not in class while working on coop, however a few students may take online classes from Northeastern while on coop.
You will pay for a total of 8 semesters tuition. You are not charged tuition while on coop. If your coop job is in the Boston area you may choose to live on campus and you would pay room and board but not tuition.
Coop is just one form of experiential learning. As a physics major you may have a paid coop job in that field or you may be doing research at Northeastern or at some research lab elsewhere.
Where are you from? If you are from Southern California or Texas, Boston will be a new experience. You will be taking the T subway around town, not driving. Northeastern is in the Fenway neighborhood of Boston across the street from the Museum of Fine Arts and near Prudential Center, Harvard medical area and many other schools.
Boston is a big city and like every big city there is noise, congestion etc. Compared to many large US cities Boston has a low crime rate. The biggest negative about Boston is the very high cost of housing because so many people want to live in the city, demand is so high. As for “unfriendly” I would say the Bostonians tend to be more blunt and direct than people in other parts of the country.
Please read through these websites for information on experiential learning:
http://www.northeastern.edu/experiential-learning/
Zoom out on this map and you will see the campus and its place in Boston:
http://www.northeastern.edu/neuhome/about/maps.html
Here is a subway map. Northeastern is on the Green Line E branch:
http://www.mbta.com/schedules_and_maps/subway/
If possible you should visit, at least on admitted student days in April if not sooner.