1. The problem statement, all variables and given/known data Given data: Tom throws a stone from a cliff 20m above the water, the initial velocity is 9m/s. Calculate the time it takes for the rock to fall down. 2. Relevant equations Now, to my questions. I solved this using the equation: y = - 1/2 gt^2 But, I found myself pretty confused at the moment. Can I use any of these equations below to solve the problem? 1. 0 = -1/2 gt^2 + 20 2. 20 = -1/2gt^2 3. 20 = 1/2gt^2 4. -20 = -1/2gt^2 5. -20 = 1/2gt^2 My biggest issue is if i put y as y = 20 does that mean that I'm calculating the time it takes for the stone to do 20 metres? On the other hand, if I put y as y = 0 like i did in the first equation, am I then calculating the same thing, ''when is the stone in the water'' What is actually the difference between these two? Thank you!