In the equation for centripetal force, which expression represents the centripetal acceleration of the object?

Second  Newton's law states acceleration of an object is proportional to the force that acts on the object and inversely proportional to the mass of the object.
We can write it down like this:

Now, let us take a look at the equation of a centripetal force:

Now we simply apply Newton's second law:

Basically, whenever you have a force and you want to find the acceleration you just divide the force with mass.

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Alkaline earth metals are found in group 2 of the periodic table.