15 weeks / semester * 2 semesters = 30 weeks. $5000 / 30 weeks = $166 / week. At $8 an hour, that's 20 hours a week; at $10 an hour it's 16 hours. (Ignoring taxes, which are low but still push the hours needed higher.)
This is not accounting for summer jobs, but my original point was that having the student contribution at that level will make some students take a paying but dead-end summer job over an unpaid internship or other opportunity that would benefit them more in the long run. (Another reason unpaid internships are questionable ethically...)
And there are plenty of off-campus jobs (SAT tutoring, etc) that can pay $35+/hr.