A stone is thrown vertically upward from ground level. It passes the edge of a balcony that is 12m above the ground with a speed of 10ms−1 on its way up, and later passes the same edge while coming down.
(i) Find the initial speed with which the stone was projected.
(ii) Calculate the time interval between the two instants when it crosses the balcony edge.
(iii) Determine the speed of the stone when it finally returns to the ground.