How this calculator works
Only the vertical component of launch velocity affects flight time when air resistance is absent. The positive root of the vertical-position equation gives the landing time; a launch from ground level with no upward velocity has zero free-flight duration. Initial height adds falling time. Inverse modes require a strictly positive time and a physically possible speed, angle, height or gravity.
Formula
0 = h0+vy T-gT^2/2; T=(vy+sqrt(vy^2+2gh0))/g; vy=v sin(alpha).
Worked example
A launch with vy = 6 m/s at g = 10 m/s2 from ground level lasts 1.2 s. A horizontal launch lasting 2 s at the same gravity must start 20 m above the landing plane.
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Frequently asked questions
Does horizontal speed affect the time?
No. It changes the horizontal range while the vertical motion determines landing time.
Can I launch downward?
Yes. Enter a negative angle or vertical component and a positive starting height.
Why can speed be impossible to recover?
At a horizontal launch angle, changing speed does not change fall time, so time alone cannot determine speed.