How fast will the rock travel 3 seconds after being dropped

Acceleration due to gravity is 9.8m/s per second. During the next second you are already falling at 9.8m/s and accelerating to 19.6m/s. So you fall another 9.8 meters, plus 4.9 meters to account for the acceleration. During the third second, you fall 19.6 meters plus 4.9 meters to accout yet again for acceleration.

Explanation:

it is the most commonly accepted one

while cooking a piece of 1/2 pound beef steak, a cast iron pan (2.4kg in weight) was heated 260 celsius.