The problem of mass: physics or philosophy?

I offer habrah citizens such a task. She once had the imprudence of telling a physics teacher. I think we can safely attribute it to the section of tasks that are set by companions at the Google interview. Here again, the answer is not important, but how the person decides it.

So imagine that you boarded a plane and carried a sandwich with you. How will the weight of the aircraft (with the content, of course) after you eat a sandwich?