A hoe weighing 8 tons is on top of a flatbed trailer and heading east on Interstate 70 near Hays, Kansas. The extended shovel arm is made of hardened refined steel and the approaching overpass is made of commercial-grade concrete, reinforced with 1 1/2 inch steel rebar spaced at 6 inch intervals in a criss-cross pattern layered at 1 foot vertical spacing.

Here's a question for you: When the shovel arm hits the overpass, how fast do you have to be going to slice the bridge in half? (Assume no effect for headwind and no braking by the driver.)



Extra Credit: Solve for the time and distance required for the entire rig to come to a complete stop after hitting the overpass at the speed calculated above.



The accident forced an 11-day closure of the eastbound lanes of Interstate 70. (The bridge itself remained closed even after the highway reopened.) The driver of the rig was uninjured, although he was later cited for not having clearance to drive on the interstate.



The Kansas Department of Transportation said the construction company for which the driver worked would be liable for the cost of repairs to the overpass, which were estimated at $134,000 as of late March 2006.