Motion System Design

Couple's skate

Finagle J. Wurme is thrilled to be visiting the roller rink for the first time. After he dons his pair of new roller skates, he moves gingerly towards the rink. He joins the others on the shiny floorboards, and gazes at them as they zoom past, the flashing lights and organ music making everything seem like it's moving at a much faster speed.

After five times around the rink, he begins to feel more comfortable and picks up speed. As he passes the rink entrance, however, a beautiful skater comes gliding onto the floor. Finagle can't take his eyes off her graceful figure until it's too late. They are headed for a sure collision course! Rather than fall at her feet, Finagle grabs onto her arms and they ride across the floor together.

If Finagle's mass is 83 kg and he is moving east with a speed of 6.2 km/hr, and the female skater's mass is 55 kg at a northern speed of 7.8 km/hr, what is their velocity after impact?

Win a textbook on wireless networks

The winner of this month's problem receives a copy of Wireless Networks by Giorgio Franceschetti and Sabatino Stornelli. This book — written for academia and industry — covers the physical layer of wireless communication, computing, sensing, and control. For additional information, visit or call (800)545-2522.

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