(6)A star rotates once every 55 days. It then undergoes a supernova explosion, hurling most of its mass into space. The inner core of the star, whose radius is initially 30 Mm, collapses into a neutron star only 8 km in radius. The rotating neutron star emits regular pulses of radio waves, making it a pulsar. What is the pulse rate (= rotation rate)? (Assume the core to be a uniform sphere & no external torque.)
(A)1.39×10⁵ rev/day
(B)1.78×10⁵ rev/day
(C)2.03×10⁵ rev/day
(D)2.28×10⁵ rev/day
(E)2.56×10⁵ rev/day