A running man has half the kinetic energy than a boy of half his mass has. The man speed up by 1.0 ms−1 and then he has the same energy as the boy. The original speeds of the man and boy respectively are
a) 2.4 ms−1, 1.2 ms−1
b) 1.2ms−1, 4.4ms−1
c) 4.8ms−1, 2.4ms−1
d) 2.4ms−1, 4.8 ms−1