Question

By what mechanism is a person injured when he or she falls from a significant height? Select one: a. Kinetic energy is converted to potential energy; the potential energy is then converted into the work of bringing the body to a stop. b. As the person falls, the amount of kinetic energy is converted into work; work is then converted to kinetic energy upon impact. c. Potential energy is created as the person is falling; the potential energy is then converted into kinetic energy upon impact. d. Potential energy is converted to kinetic energy; the kinetic energy is then converted into the work of bringing the body to a stop.

Answer 1

Answer:

d. Potential energy is converted to kinetic energy; the kinetic energy is then converted into the work of bringing the body to a stop

Explanation:

- When the person starts his/her fall from a certain height h, he/she possesses gravitational potential energy:

$U=mgh$

where m is the mass of the person, g is the acceleration due to gravity, h is the height.

- During the fall, the height h decreases, while the speed of the person increases, so gravitational potential energy is converted into kinetic energy:

$K=\frac{1}{2}mv^2$

where

m is the mass of the person

v is the speed

- Just a moment before hitting the ground, h=0, so all the potential energy has been converted into kinetic energy

- When the person hits the ground, he/she comes a stop: this means that now the speed is zero (v=0), so the kinetic energy is zero as well. This occurs because all the kinetic energy has been converted into the work of bringing the body to a stop. (the work has been done by the ground on the person)