A boy throws a rock with an initial velocity of 2.47 m/s at 30.0 degrees above the horizontal. How long does it take for the rock to reach the maximum height of its trajectory?

Answer 1

Just do the vertical problem
Vi = 2.47 sin 30 = 1.23 m/s

v = Vi - 4.9 t
at top, v = 0
0 = 1.23 - 4.9 t
solve for t

Answer 2

then divide by 2 to get the hight at time.