You shoot an arrow into the air. After 0.9 seconds the arrow has gone straight upward to a height of 30.0 m above its launch point. Ignore air resistance.
(a) What was the arrow's initial speed?
(b) How long did it take for the arrow to first reach a height of 15 m above its launch point?
The Attempt at a Solution
For the first part of the question, I tried multiple things and got wrong answers. By knowing gravity, I changed it from 9.81 m/s2 to 8.829 per .9s, then just added the 30m to 8.829.. which didn't work. I tried assuming constant acceleration, then estimated how far the arrow would have gone in 1 s, and added 9.81 m/s2. I had no idea for the second part, just assumed half the distance would take half the time, .45s was wrong.
Any assistance with this problem would be great.