There are a couple of things to notice. First, after the collision DART is moving backwards, because it bounced. Since velocity is a vector, that means that it will have a negative momentum in this one-dimensional example.
Second, the kinetic energy equation deals with the square of the velocity. This means that even though DART has a negative velocity, it still has positive kinetic energy.
We just have two equations and two variables, so these equations aren’t impossible to solve—but they’re also not trivial. Here’s what you would get if you did the math. (If you really want all the details, I have you covered.)
Illustration: Rhett Allain
Using
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