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No it isn't, you must have mistyped something. The diameter, not radius is 5mm, not that it makes a big difference. The top speed is a little over 30 meters per second or 70 mph. (Edit: possibly because you turned seconds into 1/s for some reason? Either way, the edge of the disk is not going hypersonic or anywhere close to it)

It's my fault - I misread R_d as diameter and not radius. The disc is indeed 5mm in radius (10mm in diameter). With this value, the speed of the disc edge is 65m/s or about 145mph.

Actually the radius is 5mm in the paper, it was nneonneo that got that part wrong.

The wrong part doesn't come from the 5mm, it comes from being orders of magnitude wrong by some other method.

Oh, yeah I know. Didn't mean to imply your main point was incorrect.

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