why v0 and y0 are 0? what does it mean?

Problem 3. (15 points) While standing on a bridge 45.0 m above the surface of a river, you drop a stone from rest. At exactly 1.00 s later, you throw a second stone straight downward. What initial speed must you give the second stone if both stones are to reach the surface of the river at the same instant? Neglect any air resistance effects. first stone N = D origin D 1 =0 Yo-yo = Voyt+ tant? yo so 4 5 - 0 = 0 +1( 9.8) +2 45m t = 3. 0305 sec. the second stone makes the t, = ? river ye = 45m trip in 3. 0305 sec - 1 sec = tz Xo = 2.0305 Sec. 1 stone