A ball is dropped off a roof. The ball falls for 4 seconds. Just before the ball hits the ground what is its velocity? Show work

The velocity is 39.24 m/s

Explanation:

The time of fall t = 4 seconds

The initial velocity u = 0 m/s  (since the ball is dropped, meaning it starts from rest)

Final velocity v = ?

Using

v = u + gt

where g is the acceleration due to gravity = 9.81 m/s^2

substituting, we'll have

v = 0 + (9.81 x 4)

v = 39.24 m/s

electric field is a function of 1/r^2

yes, the force per unit charge for a point charge is inverse square law.