- #1

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**
1. Homework Statement **

The problem is shown in the photo above. I would like to discuss part B.

## Homework Equations

conservation of linear momentum

## The Attempt at a Solution

the solutions say that we should have the following approach:

Mb*vb = [Mb + Ms] * vFinal.

Plug in the numbers and get vF = 0.57 m/s

However, I do not understand this. I thought that momentum is a vector and that while the block is moving forward, the slab is moving backward, so I would need to have the following:

Mb*vb = Mb*vF + (Ms* -vF)

notice the negative vF for the final momentum term of the slab. I put a negative because the slab would be moving backwards with a negative velocity.

Why is my approach not correct? I got a different vF than 0.57.

Thanks