31 October 2008

Brain Teaser Challenge - October*

Gear Heads

by Butch Shadwell

Once upon a time there lived a great green ogre in the woods at the end of the dale. From birth the children of the village were told stories of this horrible creature and what happens to those who venture too close. Because everyone in the village had been so indoctrinated from birth, no one still living in the village had been into the woods to see if the ogre was still there. The stories that had been passed down made such a journey unthinkable.
One day the people of the village were threatened with destruction as the sun was getting cooler and the winter was colder than any they could recall in over a hundred years. To get fuel to heat their homes folks had to chop trees closer and closer to the dreaded ogre’s lair. One day the inevitable confrontation occurred. As one woodcutter ventured further into the woods than anyone had before he came upon a small house. The woodcutter screwed up his courage and knocked on the door. To his relief, it was not an ogre who answered, but an average built older man with circular spectacles. Upon entering the home the woodcutter was amazed how comfortable the temperature felt, and at the array of unusual gadgets about the room.
It turns out that this wood was home to an engineer. The rumors of an ogre were started over the fact that many of the village people were afraid of math and science. It was difficult and better kept at a distance. After hearing of the village’s problems with the weather, the engineer decided to help. He told them about insulation and how to store heat in water during the day so they could use it at night. If a villager was able to heat 10000 liters of water during the day using his solar panels to a temperature of 60 degrees C, how many BTUs would be released as heat as the water cooled to 20 degrees C? It’s funny sometimes how things we fear can be worth getting to know better.
Reply to Butch Shadwell at b.shadwell@ieee.org (email)
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The names of correct respondents may be mentioned in the solution column.
* We seemed to have gotten behind on the challenges and answers. As of November, the October edition was the last one that Butch had sent out. Figure that one out:) - Webmaster.

1 comment:

Anonymous said...

Last month we discussed a thermo-dynamics problem. A rural village was trying to heat their homes a little better. “If a villager was able to heat 10000 liters of water during the day using his solar panels to a temperature of 60 degrees C, how many BTUs would be released as heat as the water cooled to 20 degrees C?”

The amount of energy released is proportional to the change in temperature. You probably remember that a calorie is the amount of heat it takes to raise the temperature of one ml of water one degree centigrade. We are using 1E7 ml of water in this problem, times 40 degrees C equals 4E8 calories of heat energy, added and then deleted from the water mass. 252 calories equals 1 BTU. So, when we divide we get 1.587E6 BTU. That’s enough heat to heat at least two homes through a freezing night. But I bet you already knew that.

- Butch