[Guest]

A 150 pound man, holding three 1 pound bricks needs to cross a wooden bridge with all three bricks with him. If the bridge can only support 152 pounds how can he transport all three bricks to the other side if he can only make one trip (and can't lose any weight)?

[Guest]

Assuming you won't let him take off his shoes, as that might be "losing weight", will you allow the man to bring a helium balloon big enough to support a pound or so? He could tie a string from the balloon, around the brick and then carry that brick (along with the other two) along with him across the bridge.

[Guest]

Juggle

[Guest]

I was also inclined to say juggle them. But depending on how high the bricks are thrown, the weight of the man + the kinetic energy transferred by catching the falling brick may exceed the 152 lb. limit. I'll admit that I haven't done the math to back that up, but it's a thought.

[Guest]

Juggling does work. According to the physical properties of juggling three objects, one object is constantly in the air. At no point is there more than two objects in the juggler's hand (assuming the juggler does Cascade or Shower technique, which are typical). However, to meet with the requirements of the bridge, the 150 pound man must start his juggling before he steps on the bridge and must not stop until he is completely off the bridge.

To address the issue of the kinetic energy...

the idea that the energy's direction would be directed downward is a valid point, and i don't feel like doing the math either.

However, to save us the hassle, the 150 pound man should just use a technique called "the claw". where he will literally release the bricks in the air and snatch them before they begin their downward decent (after the apex). Thus all energy would be potential and not kinetically transferred to the bridge.

no worries

[Guest]

juggling was my guess... born 4 baseball hit it right on.... I'm glad none of us had to do the math!

[Guest]

A 150 pound man, holding three 1 pound bricks needs to cross a wooden bridge with all three bricks with him. If the bridge can only support 152 pounds how can he transport all three bricks to the other side if he can only make one trip (and can't lose any weight)?

he can hold 2 bricks in his hand and through the third brick up. and when it comes down he should throw the other brick and catch the third stone and repeat it continuosly until he crosses the road.

[bushindo]

he can hold 2 bricks in his hand and through the third brick up. and when it comes down he should throw the other brick and catch the third stone and repeat it continuosly until he crosses the road.

Juggling sounds like the perfect option, until reality gets in the way

Juggling might allow the person to hold two bricks at any time, but consider the act of throwing a brick into the air. To hold the brick absolutely still, he has to exert 1 lb-force on the brick. To throw it up, he has to exert more than 1 lb-force, and this force is then channeled through his body and exerted on the bridge. Likewise, to stop the brick on its way down within a reasonable amount of distance, the juggler has to exert more than 1 lb-force to decelerate the brick. That combines together will exceed the 152 lb-force limit of the bridge.

[Guest]

Okay, a wooden bridge that only supports a 152 pounds. In my minds eye I see the swinging bridge that use to cross a small gully on my grandfathers farm. So I take one of the bricks and knock a couple of boards off = -a couple of pounds. I step over the gap and walk across. Or if I happen to have a couple of pieces of string with me I tie a string to two bricks, lower them on each side of the bridge to the bottom of the gully and walk then across, only lifting one brick at a time in a stepping manner. Only the weight of two bricks at a time is on the bridge at once.

[Guest]

A sterio-typical red brick weighs about 5±1lbs; 1lb bricks would be very throwable in comparison to the standard brick weight.

Unless the man is physically unfit, or the bridge is too long, I would imagine he could throw the bricks to the other side and then cross by foot.

Footballs weighing in around 1lb are thrown up to around 75m.

Shot puts weighing in around 16lbs have records of up to around 22m.

Of course the brick is less aerodynamic, and the man doesn't exactly sound like bulk of pure muscle...

But the length of the bridge has yet to be stated. It could be possible.

How long is the bridge?

[Guest]

A 150 pound man, holding three 1 pound bricks needs to cross a wooden bridge with all three bricks with him. If the bridge can only support 152 pounds how can he transport all three bricks to the other side if he can only make one trip (and can't lose any weight)?

Because of the underlined phrase I would venture that throwing would not qualify as an answer. Nor would that gully thing...although if the rope was long enough (assuming the bridge is supported by 2 posts on either side) he could tie rope around the bricks and one post, then walk over to the opposing side's post and create a pulley...though this wouldnt be crossing "with" the bricks either.

A1:

Because of the forementioned requisite, I've come up with a solution which plays on the words of the riddle abit. Assuming that crossing the bridge constitutes him stepping onto the bridge then off at the opposite side; the man places the 1 of the 3 bricks on the ground at his starting point, walks over to the opposite end with 2 bricks in hand, lays them at base of the bridge, or on the posts. Then he walks back, retrieves the last brick, walks over to the two bricks, picks them up (or touches them leaving them on the posts if that constitutes having them in his possesion) and then crosse, ideally crossing with one foot on the bridge and one foot on solid ground to avoid the magical disappearence of the bridge as a result of exceeding the weight limit.

A2:

(this is really dumb.) HE RUNS REALLY FAST.

as for taking the steps off... uh i dunno if thats such a good idea...it might create a flaw in the bridge's stability or it might simply be a stroke of genious!

Edited September 6, 2009 by Validictus

[Guest]

Juggling sounds like the perfect option, until reality gets in the way

Juggling might allow the person to hold two bricks at any time, but consider the act of throwing a brick into the air. To hold the brick absolutely still, he has to exert 1 lb-force on the brick. To throw it up, he has to exert more than 1 lb-force, and this force is then channeled through his body and exerted on the bridge. Likewise, to stop the brick on its way down within a reasonable amount of distance, the juggler has to exert more than 1 lb-force to decelerate the brick. That combines together will exceed the 152 lb-force limit of the bridge.

I agree with this. However, it may be possible if he always keeps 2 bricks in the air. I'll do some calculations and see.

Edited September 6, 2009 by psychic_mind

[Guest]

Well, I have done some calculations and actually it would not be possible.

If he uses 2 lbs of force to throw each brick for a time, t, subjecting it to 2 gs of acceleration, it will remain in the air for 2t seconds before he has to catch it again. It will take a total 2t seconds to catch and re-throw each brick. He will not have time to catch and re-throw the other 2 bricks (a minimum of 4t seconds) in that time.

[Guest]

Welcome to the boards, JonTam. Please read the sticky titled, "Important: READ BEFORE POSTING". A variation of this has been posted before.