A body of mass 5 kg explodes at rest into three fragments with masses in the ratio 1 : 1 : 3. The fragments with equal masses fly in mutually perpendicular directions with speeds of 21 m/s . The velocity of the heaviest fragment will be
A. 11.5 m/s
B. 14.0 m/s
C. 7.0 m/s
D. 9.89 m/s