A cheetah starts at rest (0 m/s) and accelerates to 26.7 m/s. It took 3 seconds for the cheetah to reach this speed. What is the cheetah's acceleration in m/s^2?

an ion is a charged atom or molecule. it is charged because the number of electrons do not equal the number of protons in the atom or molecule. an atom can acquire a positive charge or a negative charge depending on whether the number of electrons in an atom is greater or less then the number of protons in the atom.

it doesn't. it was imagined up in the middle ages.