When an object is placed in front of a convex lens, it creates a virtual image at -12.8 cm with a magnification of 2.85. What is the focal length of the lens?
(Unit=cm)

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 may be wrong but i think its a

what is the speed of a softball that travels 20m in 2secs

speed = 20/2 = 10 m/s