The old immovable object vs irresistable force trick

[Keith Webb]

This was emailed to me by a friend so I don't know the original source:

"Engineering Problem

A backhoe 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.


Solve: 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?

Extra Extra Credit: How much to the nearest $1000 did this cost the
company
moving
the backhoe and how many minutes from the time that it happened to the
time
that the
truck driver was fired for being an idiot?"