When an explosion breaks a rock, by the law of conservation of momentum, initial momentum is zero and for the three pieces, Total momentum f the two pieces 1 kg an 2 kg =√122+162=20kgms−1 The third piece has the same momentum and in the direction opposite to the resultant of these two momenta. ∴ Momentum of third piece =20kgms−1 Velocity =4m−1 ∴ Mass of the 3rd piece =