Two particles of mass m1 and m2 in projectile motion have velocities v1 < v2 respectively at tine t=0. They collide at time t0. Their velocities become v1′ and v2′ at time 2 t0′ while still moving in air. The value of ∣∣∣∣(m1v1′+ m2v2′) − (m1v1 + m2v2)∣∣∣∣ is