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.
Yes, you can neglect friction.



















I couldn't solve it either......but who cares?

 

That's more of a physics question

 

did you try to attach images?

You need to know at what point the concrete will start to fail (in compression).

You know everything to get the energy of the backhoe, except speed (KE = ˝ M (V squared)).

Once you know the energy required to cut through the concrete, you plug that number into the above equation and solve for speed.

As for the extra credit, you can't solve it with the given information. If there's no friction, the truck will never stop unless the driver applies the brakes, which it says he doesn't. You should be able to figure out.....






Wait a minute, just re-read the problem and you can't solve it. It doesn't tell you how wide the overpass is!!

- NCSU

 

Wow, someones taking engineering at NCSU

 

whats the yeild strength of the arm, concrete, and rebar. how long is the bridge, how tall is the bridge, how wide is the arm.

lots of ungiven info

 

Who would care? they ones that were involved in this.

http://www.highbeam.com/doc/1P2-592262.html

 

Graduated in '05 with a Mechanical Engineering degree

- NCSU

 

come on now dont be looking at my test!!!

as for the extra credit(if given the dimensions of the bridge) it would take engery to break the concrete and steel which would take away your KE therefore slowing you down

 

Big game on the 31st, Can yall do it?

 

How many nerds does it take???? The thread is still young.

 

Right, that's where I was going when I realized they never gave the dimension of the bridge. So the answer for distance would just be however wide the bridge was, and the time (assuming a constant deceleration) would just be d=˝ a (t squared).

In which case you'd solve for acceleration, which would be the speed of the truck before impact (minus the final speed, which in this case would be 0), divided by the time it takes to plow through the bridge. Plug that into the above equation and you'd get:
d=˝ V t where;

d=The width of the bridge
V= the speed of the truck before impact
t= time

and then solve for time.

- NCSU

 

NCSU du u speeka engliesh? No only kidding see when you take the aprox. timing of the vehical entering the bridges natural energy forcefield and the bottom of the bridge and way too low, and the top of the truck is way to high then the equation will result in a B minus of devastation. I used to party in Hays kansas it was a pretty nice place.

Only goofing, but seriously I am assuming that your degree surfaces around the ideal of creating/engineering modern facilities to be alot more stable and last through more events correct? I mean knowing how much force needed here, so that you can place reinforcement there is what the entire engineering purpose is about? You guys do alot of bridges and man made types of reinforcements for the Earths most natural resources right? I am currently guarding prisoners for a living and I honestly believe I would love to work in a field such as this. Not only does it take a genus for the properties of the job but I would also imagine it takes a high degree of common sense as well?

 

Problem is incomplete...

Mass/weight of the flatbed truck? for total moving mass would be needed.
Speed of truck.
Missing bridge size already noted.

too many missing variables.

 

Personally, I don't do that type of work, but that's the general idea behind Civil Engineering. As a mechanical engineer I studied more about how physical forces act. That is to say, if you push or pull on one part of an object, how does that affect other parts of that object (think engines, levels, all types of machines). Also studied about heat transfer, how things are affect by heating and cooling, and what affects the rate of heating or cooling. We also look at how fluid moves (think hydraulics here).

Doesn't take a genius, but it does take alot of studying and hard work. Once you get out of school, computer's take care of all the hard math. Common sense is CRITICAL to being a good engineer. I think that's what separates the successful engineers from those who just managed to get the degree.

It's a home game, so that helps, but I've lost much of my faith in both BB and FB. I think it was a huge mistake to get rid of Herb Sendek, he was a great coach, he's players graduated and for the most part behaved themselves. I think Lowe needs to go.

The new QB is the little spark of hope I need to get back into NC State football again. Too bad he got hurt in the bowl game or we would have easily won that one.

- NCSU

 

speed is what were looking for