A spherical surface of radius of curvature \( R=20 cm \) separates two media as shown in figure. Two particles \( A \) and \( B \) are moving with equal speed of \( 10 m / s \) as indicated. At a certain instant, the two particles are at equal distances of \( 20 cm \) from the spherical interface. At this instant relative velocity of \( A \) as seen from \( B \) is
(1) \( 20 m / s \)
(2) \( 40 m / s \)
(3) \( 50 m / s \)
(4) \( 60 m / s \)
