You insert the battery and the helicopter hums to life. You climb in. Has the zombie nightmare finally come to an end? Suddenly you hear a hollow laugh coming from outside the helicopter. A horrifying Zombie Newton is holding onto the helicopter! With his evil zombie strength, you're never going to get off the ground! Zombie Newton makes you a deal.

"It was I who scared off those other zombies. I take pleasure in giving my prey a chance to prove their worth before I feast on their grey matter. Answer each of my three questions correctly, and you may leave. Answer any of them incorrectly and I will eat your brains!"

Knowing this is about as good of a deal as you'll get from an undead Physics great, you decide to play along.

"Well then let's get started. If I throw a zombie walrus into a lake, and he floats with half of his body above water, how dense is the walrus compared to the water?"