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I saw that in the neighborhood a person fell our of 25th floor down the street (ground floor). I was intrigued by some questions about such situation, but all of them are out of one question: What's the velocity of a person falling from a building, in terms of km/h. Is it dependent upon the weight of the person? How to approach such a question logically and physically? I have a very little background in physics, so kindly explain it to me simply, please.

Daddy Kropotkin
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What's the velocity of a person falling from a building?

Let's first examine free-fall motion, where we assume that the person can be treated as a particle (which is fairly reasonable since the Earth is much much much larger than the person), and we assume that we can neglect air resistance, then the speed of the body after it has fallen for time $t$ under gravitational acceleration $g$ is governed simply by the kinematical relation,

$$ v_{f} = v_{i} + gt$$

and $v_{i}$ is the initial velocity of the person, and the time of their fall over a distance $h$ can be calculated from the kinematic relation,

$$ h = v_{i}t + \frac{1}{2} g t^{2} $$

where we've assumed that the direction the person is falling is the positive direction of motion.

If we want to include air resistance as a force resisting the falling person, then we would need to use Newton's second law to find the acceleration and then use that to find the velocity. See here for instance.

Is it dependent upon the weight of the person?

In free-fall motion - the case without air resistance - the velocity does not depend on the mass, as dictated by the equivalence principle. However, if we include air resistance, then the weight of the falling person is relevant.

Daddy Kropotkin
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