Motion System Design

Sliding scale

Finagle J. Wurme is in the first week of his summer job, working for the volunteer fire department in Rattlesnake Gulch. Having passed his training on the town's three-tone warning system, he commands a mobile unit, making daily rounds and searching for safety violations.

Wurme's having a soda when the day's first call goes out. He recognizes by the siren's tone that someone's reported a pest, probably a mountain lion, so he hops in his truck and drives cautiously to the outskirts of town. En route he hears a second alarm at a lower pitch, indicating a fire. Fires take precedence, so Wurme turns his vehicle around and heads back toward the station. As he contemplates the routine for donning his gear, he's interrupted by an even more ominous sound, a tornado warning. Not one to take chances, Wurme picks up the pace and drives to the nearest shelter. On the way, he realizes something's amiss when he hears an 880-Hz tone, which isn't even in the system.

If the fire station and warning siren are in the center of town along the main road, about how fast did Wurme drive responding to each call? Assume the same call went out each time, and the road is perfectly straight. The pest signal is 800 Hz, the fire signal is 775 Hz, and the tornado warning is 840 Hz. Wind velocity is zero.

For a chance to win a prize, send solutions to [email protected] by July 5, 2006. May's solution can be found on page 46.

Win a spectrum analyzer

The winner of this month's problem receives a 2.4 GHz spectrum analyzer — The Wi-Spy — from MetaGeek LLC, Boise, Idaho. It tracks and records wave frequencies possibly interfering with a wireless network. For additional information, call (208) 284-4080 or visit

2.4 GHz Spectrum Analyzer Features

  • Troubleshoots interference from Wi-Fi (802.11 b/g/n), microwave ovens, cordless phones, and Bluetooth

  • Wi-Spy software displays many wave types, stores real-time data, and analyzes current, average, and maximum signal strengths

  • Runs on Windows, Linux, and Mac operating systems

  • USB key device is about the size of a small flash drive

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