A ball of mass 3 kg moving with a velocity of 4 m/s undergoes a perfectly-elastic direct-central impact with a stationary ball of mass m.

Q. A ball of mass 3 kg moving with a velocity of 4 m/s undergoes a perfectly-elastic direct-central impact with a stationary ball of mass m. After the impact is over, the kinetic energy of the 3 kg ball is 6 J. The possible value(s) of m is/are

             (A) 1 kg only         (B) 6 kg only              (C) 1 kg, 6 kg             (D) 1 kg, 9 kg

Ans: 1 kg, 9 kg