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Rydberg formula - For hydrogen

The Rydberg formula is used in atomic physics to describe the wavelengths of spectral lines of many chemical elements. It was formulated by the Swedish ... more

Compound machines (mechanical advantage)

A compound machine is a machine formed from a set of simple machines connected in series with the output force of one providing the input force to the ... more

Speeds and feeds - Spindle speed

The phrase speeds and feeds or feeds and speeds refers to two separate velocities in machine tool practice, cutting speed and feed rate. They are often ... more

Worksheet 341

The aweÔÇÉinspiring Great Pyramid of Cheops was built more than 4500 years ago. Its square base, originally 230 m on a side, covered 13.1 acres, and it was 146 m high (H), with a mass of about 7×10^9 kg. (The pyramid’s dimensions are slightly different today due to quarrying and some sagging). Historians estimate that 20,000 workers spent 20 years to construct it, working 12-hour days, 330 days per year.

a) Calculate the gravitational potential energy stored in the pyramid, given its center of mass is at one-fourth its height.

Division
Potential energy

b) Only a fraction of the workers lifted blocks; most were involved in support services such as building ramps, bringing food and water, and hauling blocks to the site. Calculate the efficiency of the workers who did the lifting, assuming there were 1000 of them and they consumed food energy at the rate of 300 Kcal/hour.

first we calculate the number of hours worked per year.

Multiplication

then we calculate the number of hours worked in the 20 years.

Multiplication

Then we calculate the energy consumed in 20 years knowing the energy consumed per hour and the total hours worked in 20 years.

Multiplication
Multiplication

The efficiency is the resulting potential energy divided by the consumed energy.

Division
Drake equation

is a probabilistic argument used to estimate the number of active, communicative extraterrestrial civilizations in the Milky Way galaxy

... more

Proper motion (declination)

Proper motion is the astronomical measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the ... more

Holding period return

In finance, holding period return (HPR) is the total return on an asset or portfolio over the period during which it was held. It ... more

Proper motion (right ascension)

Proper motion is the astronomical measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the ... more

Dividend discount model ( Gordon growth model)

The dividend discount model is a method of valuing a company’s stock price based on the theory that its stock is worth the sum of all of its future ... more

Wiswesser's rule

The Wiswesser rule gives a simple method to determine the energetic sequence of the atomic subshells (n,l). n is the principal quantum number and l is the ... more

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