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I have a question about momentum that showed up in my physics textbook. It's a True/False question, and I have the answer, it's just that I'm not sure how it works. Could someone please explain this to me? Many thanks.

|Glider 1|-----> <------|Glider 2|

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Air Track

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Statement: In an isolated system, two gliders (m1 = m2) on an air track move toward each other at equal speed, collide, and then move away from each other at equal speed.

Question (T/F): For this collision, if the change in momentum of glider 1 is -1.4 kg×m/s [W], then the change in momentum of glider 2 is 1.4 kg×m/s [W].

The answer is true.

I'm not sure how the numbers even got there. I recognize that they just happen to be [tex]\sqrt{2}[/tex], so I'm assuming there's some type of calculation to be made with the formula for kinetic energy [tex]E_{k}=\frac{1}{2}mv^2[/tex]. However, I just don't see how it works. I thought that the change in momentum was simply [tex]\Delta p=2mv[/tex]