You're describing a scenario where an object has an initial momentum of 80 kg m/s and then collides with something, resulting in a momentum of -100 kg m/s.

Here's the key point: Momentum is a vector quantity. This means it has both magnitude (the amount) and direction.

Since momentum is a vector, we can't simply add the two values together like regular numbers. To find the total momentum, we need to consider the directions of the two momenta.

Here's how to approach this:

1. Define a positive direction: Let's say the initial momentum of 80 kg m/s is in the positive direction.

2. Consider the negative sign: The -100 kg m/s indicates that the momentum after the collision is in the opposite direction (negative direction).

3. Calculate the total momentum: Since the momenta are in opposite directions, we subtract them: 80 kg m/s - 100 kg m/s = -20 kg m/s

Therefore, the total momentum after the collision is -20 kg m/s. This means the object is now moving in the opposite direction (the negative direction) with a momentum of 20 kg m/s.