A stone is thrown horizontally from a tower 25 m high at a speed of 15 m / s. Determine how long the stone will be in motion.

To determine the time of the fall of a body thrown down at an initial speed, use the formula:

H = Vo * t + g * t ^ 2/2,

where Vо is the initial speed of the body,

t – fall time,

g – acceleration due to gravity (rounded up to 9.8 m / s2).

H = 25 m, Vо = 15 m / s

25 = 15 * t + 9.8 * t ^ 2/2;

4.6 * t ^ 2 + 15 * t – 25 = 0;

we solve the quadratic equation for t:

D = 15 ^ 2 + 4 * 4.6 * 25;

D = 685.

t1 = (-15 + √685) / (2 * 4.6);
t1 = 1.21 (s) (rounded to hundredths in calculations)

t2 <0.

Answer: the body fell from a height of 25 meters in 1.21 seconds.