The curve does not use an arc length as a parameter
If |v(t)| = 1, for all t ≥ a, then the parameter t corresponds to arc length.
|v| = |r'| × |v| =√4t² + 16t² + 64t²
=√84t
=2√21
It is not equal to 1, so it doesn't use arc length as a parameter.
Also,
s = √21t
r(s) =(s/√21, 2s/√21, 4s/√21)
for
√21 ≤ s ≤ 16√21
|r'(s)| = (1/√21) × √1+4+16
= 1
This is the length of a segment of an arc
In order words, an arc length is a fraction of the circumference of the circle
Learn more about arc length:
https://brainly.com/question/2005046