A stone thrown horizontally from the top of a cliff takes 4 seconds to reaxh the bottom of the cliff? What is the height of the cliff? ( g= 9.8 m/s^2)

The protons in a nucleus are approximately 2 ✕ 10^−15 m apart. consider the case where the protons are a distance d = 1.93 ✕ 10^−15 m apart. calculate the magnitude of the electric force (in n) between two protons at this distance.