Answer:
The total momentum after the collision is 1 kg-m/s.
Step-by-step explanation:
We have,
Mass of a steel sphere is 0.5 kg
It is travelling with a speed of 2 m/s
It collides with an identical sphere at rest.
The law of conservation of momentum states that the initial momentum is equal to the final momentum for an isolated system. Here, initial momentum is :

So, the total momentum after the collision is 1 kg-m/s.