At that velocity, wouldn’t it have burned up in the earth’s atmosphere like a meteor?
It appears it appears impossible for it to retain much of its initial velocity while passing through the atmosphere. A ground launched hypersonic projectile has the same problem with maintaining its velocity that an incoming meteor has. According to the American Meteor Society Fireball and Meteor FAQ meteors weighing less than 8 tonnes retain none of their cosmic velocity when passing through the atmosphere, they simply end up as a falling rock. Only objects weighing many times this mass retain a significant fraction of their velocity
But I would also expect a hurtling disc would have rapidly begun to fly like a Frisbee, and that would ease its passage through the air. If not leaving Earth, it might have sailed out of the state, eventually falling into a body of water or a woods or somewhere else it would be regarded as just another piece of junk.
You got it. This problem is among the much discussed flaws in Jules Verne's conception of a ballistic launch into space from a canon.
Of course, on entry to the atmosphere from space, the thin upper atmosphere is encountered first. Starting from the ground, it's problematical how an object can even be given an initial velocity on the order of escape velocity, and supposing that it could, it's initial encounter with the dense lower layer of the troposphere would be inconceivably violent.
That was my thought, too. It would have burned going up at that speed and if it didn't reach escape velocity it would have burned more (maybe completely) on the way down again.