Use this equation of motion to solve problems in which you do not know the final velocity
I'll show you how below.
The equation above has been derived especially for the purpose of solving a problem in which you do not know the final velocity of the object.
The first term in the equation tells us how far the object would travel in time
The second term tells us the additional distance it travels due to the acceleration. (It is the complicated part!)
So, since in your problem,
The negative sign means the object is travelling downward.
In the first 5 seconds, it falls