Two bodies of masses 2 Kg and 7 Kg are moving with velocities of 7 m/s and 2 m/s respectively towards each other. What is the total momentum of the system in Kg-m/s?

0 

Let's say they are moving along x-axis. 

$p_1 = 2 \text{ kg x } 7 \text{ m/s } = 14 \text{ kg.m/s}$

$p_2 = 7 \text{ kg x } 2 \text{ m/s } = - 14 \text{ kg.m/s}$

Total momentum : $p = p_1 + p_2$

$p = 14 \text{ kg.m/s} + (-14 \text{ kg.m/s})$

  = 0