# A body was thrown vertically upwards from a tower 15 m high at a speed of 10 m / s.

A body was thrown vertically upwards from a tower 15 m high at a speed of 10 m / s. In how many seconds will it fall to the ground?

V0 = 10 m / s.

h0 = 15 m.

g = 10 m / s2.

t -?

The body will first move vertically up to a complete stop, and then down. The body will move up and down with the acceleration of gravity g.

t = t1 + t2, where t1 is the upward movement time, t2 is the downward movement time.

The time of movement of the body up t1 and the height of rise up h1 are expressed by the formulas: t1 = V0 / g and h1 = V0 ^ 2/2 * g.

t1 = 10 m / s / 10 m / s2 = 1 s.

h1 = (10 m / s) ^ 2/2 * 10 m / s2 = 5 m.

The body will fall down from the height h2 = h0 + h1.

h2 = 15 m + 5 m = 20 m.

h2 = g * t2 ^ 2/2, where t2 is the downward movement of the body.

t2 = √ (2 * h2 / g).

t2 = √ (2 * 20 m / 10 m / s2) = 2 s.

t = 1 s + 2 s = 3 s.

Answer: the flight time of the body from the tower is t = 3 s.

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