Question

Which formula do I use?

The subject is free fall

T=45
y=?
Vf=?

Answer 1

This is a 2 part question, I think.

Explanation:

First you need to find the displacement, s from `s = u.t + 1/2 a.t^2` where u is the initial velocity (often zero, the wording of the question may indicate this by using "dropped" or "falls".) This may have been defined for you as `v_i`?

Next, you use the fact that you now have the displacement, initial velocity and acceleration to find the final velocity, `v_f` using:

`v_f^2 = u^2 + 2a.s`

That should work, but a cleverer person may suggest a simpler (better) method.