Abubble originating at the bottom of a lake rises to the surface within 10.0 seconds with an acceleration of 10.0 meters/second2. what is the depth of the lake?
100 meters

I KNOW that you must have seen this formula before.  It gives
the distance covered in a certain time of accelerated motion:

               D  =  1/2  A  T²

     Distance covered= (1/2) (Acceleration) (Time squared) .

The question gives us the acceleration and the time.
I've got a weird idea:  Let's plug them into the formula.  OK ?

       Distance = (1/2) (10 m/s²) (10 sec)²

                       =      (5 m/s²)      (100 sec²)

                       =              500 meters  .

           Deep lake !