An object in the solar system could be identified if it appeared to move from its place in the earlier photograph.

VOA: special.2010.07.11

And know intuitively that if they move together, they will behave like an object of mass 5 and the acceleration will again be 2.

凭直觉认为既然它们一起运动,那么它们就相当于一个质量为 5 千克的物体,然后我们可以算出加速度为 2

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