On a train moving along east with a constant speed v, a boy revolves a bob with string of length l on smooth surface of a train, with equal constant speed v relative to train. Mark the correct option(s).
A. Maximum speed of bob is 2 v in ground frame
B. Tension in string connecting bob is `(4mv^(2))/(l)` at an instant
C. Tension in string is `(mv^(2))/(l)` at all the moments.
D. Minimum speed of bob is zero in ground frame
