You drive along on a straight road at 20 m/s. The light in front of you turns red and you brake with a constant acceleration. You come to a stop after traveling a distance of 15 meter. Assume you started out driving in the positive direction. a. What is the acceleration of the car?
b. How much time did it take to comes to a stop?

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.)