Engineering problem (attn: Kent)

[gkainz]

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 crisscross 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

Bonus Question: Compute reaction time after driver sees clearance marking on bridge. Show time delay in nearest nanoseconds between reaction time and driver realizing "I am SO fired."

 

[jesse]

Oops.

 

[tonycondon]

Ive seen this, hopefully the truck driver was wearing a seat belt, because that would be one hell of an acceleration.

 

[jason]

It happened on Valentine's Day...

I bet he wasn't in the mood to cuddle with his sweetie that night.

 

[GaryO]

Imagine driving across that bridge and seeing that in front of you <img>.

 

[ScottM]

Imagine driving across that bridge and seeing that in front of you <img>.

That is what I was thinking. I think you would first say the 'word' then perhaps 'do the word'

I know I would be asking myself about how much longer the bridge would remain standing.

 

[fgcason]

Greg,
If you hear someone to the south of you wake up screaming at 2am in the next week, that'll be me waking up from a sound sleep because of that picture. I'm already convinced every driver on the road is deliberately trying to kill me on the motorcycle...and now I have to worry about cruising along fat dumb and happy without a cage in sight and have THAT suddenly plow through the bottom of the bridge in front of me. I'll never look at a bridge the same way again.

Solve:

I would ask the driver of the truck that was hauling that particular backhoe. I'm guessing somewhere in the 70-90 range.
Reinforced concrete apparently isn't so tuff after all is it?

Extra Credit:

My guess is the cab and front of the trailer kept going a ways (in the 200-400ft range but could have been in the 100ft range) The backhoe and trailerbed appears to have just kind of stopped in about 40-50ft from whatever speed it was going. I'm guessing it took a while for the driver to get over the fact that his truck just exploded for no reason before he got on the brakes.
I wonder how the 4-5ft separation tailgater in the SUV fared in that one. Gonna need automatic velcro tires and retro rockets because ABS brakes and airbags just isn't going to cut it.

Bonus Question:

F=ma
D=rt
{then a miracle occured}
Time = 0

Scenario #1: "Another bridge ho hum. No traffic, no hassles, nothing to bump into, xxFT yyIN, no probl" BLAM!
Scenario #2: "xxFT!!! yyIN!!! IT'S TOO LATE!!!" BLAM!
Sceanrio #3: "I wish that SUV would get off my taillights so I could see where he is" BLAM! "I bet he won't do that again"

 

[wbarnhill]

{then a miracle occured}

That's my absolute favorite excuse.

 

[tonycondon]

F=ma
D=rt
{then a miracle occured}
Time = 0

that is my kind of math

 

[Let'sgoflying!]

Wow those Mythbuster guys are going to be jealous.

 

[ScottM]

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...)

I would say just a little bit faster than the speed he was going.