A lead ball is dropped in a lake from a diving board 5.13 m above the water. it hits the water with a certain velocity and then sinks to the bottom with the same constant velocity. it reaches the bottom 3.90 s after it is dropped. (a) how deep is the lake? (b) what is the magnitude of the average velocity of the ball for the entire fall? (c) suppose the water is drained from the lake. the ball is now thrown from the diving board so that it again reaches the bottom in 3.90 s. what is the magnitude of the initial velocity of the ball?