"An atomic nucleus initially moving at 420 m/s emits an alpha particle in the direction of its velocity, and the new nucleus slows to 350 m/s. If the alpha particle has a mass of 4.0u and the original nucleus has a mass of 222 u, what speed does the alpha particle have when it is emitted?"(adsbygoogle = window.adsbygoogle || []).push({});

I did [tex]222u * 420 m/s + 0 = 222u * 350m/s + 4 u * X m/s[/tex] and I get 3885 m/s, but the answer says it's 4200. What did I do wrong?

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# Particle Momentum problem

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