The equation of a wave travelling on a string is \( y = \sin[20\pi x + 10\pi t] \), where \( x \) and \( t \) are distance and time in SI units. The minimum distance between two points having the same oscillating speed is:
\( 5.0 \, \text{cm} \)
\( 2.5 \, \text{cm} \)
\( 10 \, \text{cm} \)
\( 20 \, \text{cm} \)