Question

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?

Answer 1

2.5

Step-by-step explanation:

Answer 2

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)