So my 3.84 ms-1 is way out.
A baud rate of 300 can transmit 30 signs a second wikipedia says, so 9600 should be enough.
So, every 2.5mm the cord moves, you receive a character.
The character takes around half a millisecond to transmit.
You then print a floating point number with four places after the decimal and a newline, and each character takes around 1 millisecond.
You do the arithmetic.