You drop a rock down a well that is 31 m deep. how long does it take the rock to hit the bottom of the well?

In order to keep this problem simple, we can assume that the acceleration
of gravity is constant over the distances involved ... 9.8 m/s² . 

(When you get super-technical about it, once you go below the surface
of the Earth, gravity actually decreases the deeper you go.)

A useful formula here is:

                 Distance in free-fall  =  (1/2) (gravity) (time)²

                                     31 m      = (1/2) (9.8 m/s²) (time)²

Divide each side
by    4.9 m/s²  :            31 m / 4.9 m/s²  =  time²

                                     31/4.9  s²  =  time²

Square root each side:      time  =  √(31/4.9)  s

                                                      =  2.52 sec  (rounded)

                                  

The radiation of the fire causes the saucepan to heat up. the conduction of the saucepan then to distribute the heat over the saucepan and to give heat to the water. the convection of the water distributing the heat within the water, till all the water is boiling