What is the acceleration of the object 0 m/s

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 ?

It is really hard for me right know

Acalorimeter uses the principle that thermal energy flows from hotter material to colder material until both reach the same