Another Clever Riddle

[d3z]

*sigh* I feel compelled to be the biggest dork ever....so here i go (I had to do this stupid problem in highschool physics)

The horizontal component of motion can be eliminated (we'll assume a flat bridge, since a sloped bridge would affect the problem).  Any horizontal component of force has no effect on the downward force on the bridge (this isn't completely true in real life).

Once a bar of gold is in free-fall (in the air), it's weight has no bearing on the force John applies to the bridge.  Let's assume that the bar is freefall for time 't'.  During this time, gravity has applied a constant downward force of 1g.  In order for the bar to have the same ending state as when it started, John had to apply the same acceleration to the bar (partly during the throw, partly during the catch, both equal if he catches it at the same height he released it on the throw).  The integral of this force over time across the bridge will be equal to the force of the static system (81*g).  Since we know that when the bar is in freefall, and therefore the force on the bridge will be less, it must be greater when John is throwing or catching.

John can carefully move himself up and down in opposition and balance this force out, but I doubt this is something a human could coordinate.  In any case, the best he can do is limit the force to 81*g.  In all likelihood, the juggling will only make matters worse.

[jesusfreak]

 In all likelihood, the juggling will only make matters worse.

But it would look oh so cool

--
lucas

[al Hartman]

 momentum is calculated from the velocity and the mass, and the amount of force exerted by a given momentum is some sort of moment of impulse calculus calculation, i think.

i am such a dork

brian

     No, Brian, you're certainly no dork.  A heretic, possibly, but not a dork.  You see, this isn't a question of religion, so it was just wrong of you to try to involve "the mass."
     Besides, the question of calculus is best addressed by a dental hygienist.

     You guys are all leaving out all kinds of important variables.  Is it light outside or dark?  Is there a breeze, and if so, what is its direction?  In fact, in what directions does the bridge run?  And in which of those directions is the dude with the gold traveling?
     Does the bridge cross over a dry gulch or over water, and if over water, is it flowing or still?  Of what substances is the bridge composed and what is its architectural style?  How near the bottom of the bridge is the water or land beneath it?
     What is the season of the year?   Is the weather wet or dry?  In what phase is the moon, and what is the alignment of the planets?  How much wood could a woodchuck chuck?  Where's the peck of pickled peppers that Peter Piper picked?

     I know, at this point all you genii suppose that I'm just making fun of you because I can't keep up with your ideas...  Hah!  
     Just consider:  If the bridge is of a simple truss design, made of wood, and crosses a stream which has been backed up by a clogged beaver dam until the water's surface is touching the bottom of the bridge, and these conditions have remained constant well into a cold winter which has frozen the water's surface to a depth of, say, a foot, while the dark of night and a stiff breeze have seen to solidifying what slight melting the day's sunlight may have produced, well...  this guy can juggle his gold or his checkbook while he crosses the bridge in an Abrams tank & be safe.  Nothing short of a direct bomb strike is going to break that bridge.
     On the other hand, if an extremely wet spring has eroded away the supporting ground at both end of the bridge, the thaw to the north has caused the creek beneath to become a rushing torrent which is now slamming broadside into the bridge's lowest two feet, and the winds are approaching hurricane velocity at the same cross-direction to the bridge as the water, a mouse wouldn't want to set foot on it, 'cuz it's gonna go at any second...

     Eulaha, please find another thread to post on-- this is giving me a splitting headache, and I haven't slept since Saturday!!!  Some of us find this stuff addictive...

al