a stone is droped from a building of height h and it reaches ground after t sec.from the same building if two stones are thrown ( one upward and one downward ) with the same velocity u and they reaches the earth after t1 and t2 sec reapectively,then 1) t=t1-t2 2)t=(t1+t2)/2 3)t = √t1t2 4)t=t1²t2²