3.43Q

[Vienna]

How come the displacement of the ball won’t be 4m?

[FizziksGuy]

Exactly .7 seconds after the ball is released, you don't (yet) know how far it has fallen.  You could solve for the displacement of the ball after 0.7 seconds, however.

 

If, instead, the problem had asked "how fast is the ball traveling the instant before it hits the ground," in that case you would use 4.0 meters as the displacement, but you would not know t (elapsed time).