Standing at the top of a 30.0 m high cliff, you throw a rock straight down with a velocity of 8.00 m/s. after how many seconds does it hit the ground?

It will take 1.789 sec  

Explanation:

We have given height h = 30 m

Initial velocity u = 8 m/SEC

Acceleration due to gravity

Now according to second equation of motion

After solving we get t = -3.42 sec and t = 1.789 sec

As negative time is not possible so time will be 1.789 sec

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.

answer; (arch); good luck