LED Lighting January 2010

You probably noticed the increase use of LEDs for Christmas lighting. LEDs are beginning to be used in traditional applications for the home. EarthLED thinks that they can produce a LED “bulb” that will be equivalent to a 100 watt incandescent bulb for a suggested retail of $80. The LED will use 12 watts. An incandescent bulb sells for $1. The LED is expected to last 50,000 hours while an incandescent bulb will last 1000 hours. A kilowatt hour cost 8 cents. Prepare a cost analysis for the most used light bulb in a typical household which has an average use of 5 hours a day.

Archways November 2009

Archways are a popular feature in many construction projects. Many older archways were created using stones called keystones. In the photo above, an archway is shown with the setting of a keystone at the top of the arch.
Archeologists have unearthed a stone from an archway built many years ago. The stone is 25 inches thick. The front surface is in the approximate shape of an isosceles trapezoid. The longer base is 16 inches long and the shorter base is 12 inches long. The legs measure 24 inches. Archeologists know that typically all the other stones in the archway were congruent to the stone that was found. How many stones similar to the one described would it have taken to produce the original archway? What was the interior diameter of the archway?

Water Cistern October 2009

In Shaker communities of the past, cisterns were built to store water as shown in the photo above. They were built as a cylinder with a hemisphere on each end partially buried underground. The diameter was 10 feet. The water was collected from large barn roofs. Even today, cisterns are still used extensively. Using the Shaker design described above, calculate the size of a cistern so that it could hold all the collected water from a 90 ft by 150 ft barn roof given a 20 inch rainfall. How many gallons will your cistern hold?

Drippping Faucet September 2009

Water is one of our most valuable resources. Many times it is wasted without us even thinking about it. Suppose a faucet leaks one drop per second. How much water will be wasted by the leak in one year? How many feet of half inch water pipe would that equal? Design an experiment to find the answer.