Physics, 04.03.2020 23:24 sim2004

A boulder is raised above the ground, so that its potential energy relative to the ground is 200 J. Then it is dropped. Estimate what its kinetic energy will be just before hitting the ground.

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Answer from: srsnider2017

200 J

Explanation:

In this problem, I assume there is no air resistance, so the system is isolated (=no external forces).

For an isolated system, the total mechanical energy is constant, and it is given by:

E=KE+PE

where

KE is the kinetic energy

PE is the potential energy

The kinetic energy is the energy due to the motion of the object, while the potential energy is the energy due to the position of the object relative to the ground.

At the beginning, when the boulder is raised above the ground, its height above the ground is maximum, while its speed is zero; it means that all its mechanical energy is just potential energy, and it is:

$E=PE_{max}=200 J$

As the boulder falls down, its altitude decreases, so its potential energy decreases, while the speed increases, and the kinetic energy increases. Therefore, potential energy is converted into kinetic energy.

Eventually, just before the boulder hits the ground, the height of the object is zero, and the speed is maximum; this means that all the energy has now converted into kinetic energy, and we have

$E=KE_{max}=200 J$

Therefore, the kinetic energy just before hitting the ground is 200 J.

Answer from: Quest

scattering of light by tiny particles in air to produce the colors we see on sky, is dependent on the following factors:

(i) wavelength of light

(ii) size of the scattering particle

(iii) distance traveled by light through the atmosphere.

according to rayleigh's law of scattering, the amount of scattering is inversely proportional to the fourth power of its wavelength. shorter the wavelength, greater is its scattering. hence violet/blue light is scattered more than red.

sun's light is a composite light ( visible light) with wavelengths in the range 400 nm (violet) to 700 nm (red). as sunlight passes through our atmosphere, the molecules of air scatter light according to their wavelengths. during sunrise and sunset, the sun's position is below the horizon. hence light from the sun travels a greater distance in the atmosphere when compared to its position a noon.

as sunlight enters the earth's atmosphere, blue light is scattered away and at the end of its journey in the sky, only red and orange wavelengths remain in the beam.

hence at sunrise and sunset, the sky appears reddish orange.

Answer from: Quest

high-sugar diet and high cholesterol

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A boulder is raised above the ground, so that its potential energy relative to the ground is 200 J....