For a travelling harmonic wave:
\(y(x, t) = 2.0 \cos 2\pi(10 t - 0.0080 x + 0.35),\) where \(x\) and \(y\) are in cm and \(t\) in s. The phase difference between the oscillatory motions of two points separated by a distance of \(0.5\) m is:
1. \(8 ~\pi \text{ rad}\)
2. \(0.08~ \pi \text{ rad}\)
3. \(0.008~\pi \text{ rad}\)
4. \(0.8 ~\pi \text{ rad}\)