Depth of a pond seems shallower than the real depth, why?​

Alead ball is dropped into a lake from a diving board 5m above the water . it hits the water with a certain velocity and then sink with constant velocity in bottom . it reaches the bottom 5 second after it is dropped if g= 10m/s2 . find depth of the lake and average velocity of the ball ?

A2k pendulum has a speed of 1 m/s at a height of 1/2 meter

Which situation will produce the greatest change of momentum