object a does a freefall motion from an 80-m building and object b thrown upward from the base at the same time. they collide after 2s. find the initial velocity of object b. height is 80 m.
object 1: h=80-1/2 g t^2
object 2: h=vi*t-1/2 g t^2
set them equal.
vi*t=80
solve for vi