Aman throws a pebble upward from a point on a cliff 85 m above the sea. the pebble drops into the water 6.2 s after it is thrown. assuming that air resistance is negligible, what is the velocity of the pebble just after it is thrown?
a) 11 m/s
b) 14 m/s
c) 17 m/s
d) 20 m/s
pleease with this i honestly dont understand it..

When a vertical beam of light passes through a transparent medium, the rate at which its intensity i decreases is proportional to i(t), where t represents the thickness of the medium (in feet). in clear seawater, the intensity 3 feet below the surface is 25% of the initial intensity i0 of the incident beam. what is the intensity of the beam "10" feet below the surface? (give your answer in terms of i0. round any constants or coefficients to five decimal places.)