I would greatly appreciate it if someone can clarify the conditions on when to use to each of the kinematics equations, because I end up with the wrong answer for using the wrong equations of the 3. 1. vf = vi + at When can I use this and when cannot? 2. vf^2 = vi^2 + 2a(xf-xi) When can I use this and when cannot? 3. (xf-xi) = vi t + at^2/2 When can I use this and when cannot? For example: Suppose a ball is thrown vertically upward from earth with velocity v and returns to its original height in time t. If the g value is reduced to g/6 then what would t be? Why use equation 1 which will result in a time increasing by a factor of 6. If I use the second equation time will be increased by a factor of 6^1/2 ?