A ball of mass 0.1 kg is whirled in a horizontal circle of radius 1 m by means of a string at an initial speed of 10 r.p.m. Keeping the radius constant, the tension in the string is reduced to one quarter of its initial value. The new speed is
(a) 5 r.p.m.
(b) 10 r.p.m.
(c) 20 r.p.m.
(d) 14 r.p.m.
