A ball is dropped from rest atop the roof of an apartment

 

building. The ball$$s initial height is h$0=18$ m$.$ On its way 

 

down, the ball passes by a window whose top and bottom

sides are located h$1=7\mathrm{.}0$ m and h$2=5\mathrm{.}7$ m above the ground,

respectively. What is the change in speed $$v of the ball as

it passes from the top to the bottom of the window? For the

limit check, investigate what happens to $$v if the window

becomes extremely short $($h$1->$ h$2).$