Answer:
4307 kg.m/s
Explanation:
Momentum is the product of mass and velocity of an object.
p=mv where p is momentum, m is mass of the object and v is the velocity.
Taking right direction as positive, the initial momentum of the first train car will be 590*7.3=4307 kg.m/s
We know that from law of conservation of linear momentum, the sum of initial momentum equals the sum of final momentum