*With the Capitol building behind her, first lady Michelle Obama challenged some 5,000 George Washington University graduates at their commencement on the National Mall Sunday to “keep giving” through community service work and to “keep engaging” with the world.

Mrs. Obama agreed to be their speaker only after students, faculty and staff met her challenge to complete 100,000 hours of community service.

“I have one more request to make of you, one more challenge,” Obama said during her speech. “Keep going. Keep giving. Keep engaging.”

The university said that students actually volunteered 163,000 hours in total. Obama noted many of the accomplishments: improving a Washington school, visiting with veterans, teaching English to refugees and shoveling snow during a record winter snow storm.

But she urged students to continue the work, both in the United States and abroad. She said serving would make “the world safer” and make the students “more competitive.” “So many of today’s challenges are borderless — from the economy to terrorism, to climate change … more than any other generation yours is fully convinced that you’re uniquely equipped to solve those challenges,” said Obama, who spoke for about 30 minutes. “You guys can’t be stopped. You don’t know the meaning of the word can’t. And every time someone’s tried to tell you that you’ve replied what? Oh yes, we can!” [Watch entire speech below.]

During the ceremony, George Washington University president Steven Knapp presented Obama with an honorary Doctor of Public Service degree. Pianist and composer Dave Brubeck and entrepreneur A. James Clark also received honorary degrees at the commencement.

Saturday’s speech was not the only commencement address the first lady has given this year. Earlier this month she spoke at the historically black college University of Arkansas at Pine Bluff. [Watch clip below.]

Obama, who graduated from Princeton and Harvard Law School, will also speak next month at the graduation of Anacostia Senior High School in Washington, a public school she visited last year as part of her mentoring program for young women.