who can solve this physics problem?

[buddyjuf]

Originally posted by rnicey
There is an upwards force, it's what makes terminal velocity, erm, terminal. Otherwise you'd keep speeding up.

yeah? the birds will be speading up @ 9.8m/s(2)?

[Excellence]

When they land, you're busted.

[xxxdesign-net]

Originally posted by BV


nope, i disagree

if the birds let themsleves fall... and the bird are aerodynamic... the air/pressure will be pushed.. a bit downward but mainly horizontaly.... (or downward with angles... which will end on the sides...)

[buddyjuf]

Originally posted by Excellence
When they land, you're busted.

in theory, you will have reached the other side of the bridge when they fall

[buddyjuf]

Originally posted by xxxdesign-net



if the birds let themsleves fall... and the bird are aerodynamic... the air will be pushed.. a bit downward but mainly horizontaly....

granted, but the force will be SO small, its impossible it will be half of the birds weight, dont you agree?

[Excellence]

Here's a phsics question for you. How do you get 5 haitians in a shoe box?

[rnicey]

Originally posted by bdjuf


yeah? the birds will be speading up @ 9.8m/s(2)?

Only if they've been compacted into golf ball shapes. Remember a tonne of lead and a tonne of feathers may be the same mass, the lead will hit the ground first not because of it's mass but because of it's wind resistance. They proved this on the moon, the feather and the metal bar hit the ground at the same time because there (and not on Earth) there wasn't any drag force.

[buddyjuf]

Originally posted by rnicey
Only if they've been compacted into golf ball shapes. Remember a tonne of lead and a tonne of feathers may be the same mass, the lead will hit the ground first not because of it's mass but because of it's wind resistance. They proved this on the moon, the feather and the metal bar hit the ground at the same time because there (and not on Earth) there wasn't any drag force.

absolutely, that has to do with the resistance of air
but as I said right before you posted this, that force of resistance will be so small, impossible to be half the birds weight in the first few seconds / milliseconds of falling

[buddyjuf]

and as someone previously said, a birds shape is aerodynamic, therefore making the resistance of air extremely low, compared to if they would be feathers falling, for example.

[buddyjuf]

anyways, I am off to bed
it was very nice debating with you guys
cya in the morning!

[rnicey]

Originally posted by bdjuf


interesting point
what if the holes were on the ceiling of the truck?

Side, ceiling, even better. Think of it like a helicopter, it's pushing air down so it can stay up. It's got to get that air from somewhere else, usually above it. Another way to think of it is those cartoons where the character is climbing up a falling ladder (which works if you're really really quick about it). If you only have ladder above you and it vanishes or has nowhere to go below you you're going to fall.

[rnicey]

Originally posted by bdjuf


absolutely, that has to do with the resistance of air
but as I said right before you posted this, that force of resistance will be so small, impossible to be half the birds weight in the first few seconds / milliseconds of falling

Weight has nothing to do with it. A parachute weighs what, 10-20 pounds, they drop real slow when open, real fast when closed. Same weight.

Birds are aerodynamic (in one direction), but they are also lightmass and horribly un-aerodynamic for vertical lift. The resistance (force) is great, that's how they can glide.

[buddyjuf]

Originally posted by rnicey
Weight has nothing to do with it. A parachute weighs what, 10-20 pounds, they drop real slow when open, real fast when closed. Same weight.

Birds are aerodynamic (in one direction), but they are also lightmass and horribly un-aerodynamic for vertical lift. The resistance (force) is great, that's how they can glide.

and what if they fall down the same way that they would usually fly? beak on the bottom?

[(¤¤)»»»»»»Þ]

Your all wrong they make those signs to cover 25% more than what is the REAL max. So he just drives across the bridge and doesnt worry about it while everyone else sits on their asses trying to figure a way across..

OR

You throw the chickens in the back of another guys truck thats doesnt weigh as much

[fiveyes]

Originally posted by bdjuf
and the ONLY way to make it past the bridge
is if you make the birds do FREE FALL while your passing the bridge

that is the only way that they will not be exerting a force on the truck floor

as I said, its theoretical, not practical, so it would be almost impossible to do this in real life, unless your car goes EXTREMELY fast and the bridge is EXTREMELY short

but the theory is there

once again, if the birds do free-fall, there is no force on the floor, so its an easy 900kg passing the bridge of 1000kg capacity

thank you all for playing

You've overlooked one thing- in free fall, the birds would be falling straight down but the truck is moving forward across the bridge. And, as soon as the back of the truck hits the birds, their weight gets added if they're going to cross that bridge.

Closed systems are what closed systems do. Nice try though, bdjuf, you had a couple of 'em going there...

[Muff]

Just tell half of the birds to jump in the air. Tell the other half to jump before the other birds have landed. Rinse and repeat.

Or just kill half of them? Who needs that many trick birds anyways?

[(¤¤)»»»»»»Þ]

Or you could tie all the chickens together by the legs and tie the first one to the back bumper and just drag them ..

Or you do a dukes of hazzards and just jump the damn bridge

[quantum-x]

wtf?

yes, actually
think of it when a helicopter takes off, the propeler exerts a force greater than its weight onto the ground to lift off. and in order to stay flying, must exert the same amount of force as its own weight. otherwise it will drop.

what type of crazy pyhsics is this?

the ground is not exerting a force on the helicopter. gravity is exerting a force. to lift off the ground, you have to exert a force greater than gravity to take off.

this business about exerting a force to the ground is crap!

think about it in these terms. say 'i exert' 900N to the ground. I want to take off, so by that reasoning, i have to "exerts a force greater than its weight onto the ground to lift off" ,so i go and find another 900N person and hold them up? pfft.

[DirtyDanza]

birds fly while your driving..... reduce the weight load

[CoolE]

You tell the birds to dig their claws into the bed of the truck and flap as you cross the bridge. If you have trained them well and they are in shape then you just might fly across that bridge.

[404]

ok brainiacs...

assume 2 people, each having a weight tied to the end of a length of rope, swing the rope from above their heads as fast as they can, then let it slow under its own momentum. if one weight is twice as heavy as the other, which will be the last to stop...the heavy or the light one?

i'd have said the heavy one would stay rotating the longest(thinking along the lines of a car's flywheel) but i'm assured by others the heavy one would slow and stop the quickest.

[rnicey]

Originally posted by bdjuf


and what if they fall down the same way that they would usually fly? beak on the bottom?

It'd have to be a real short bridge for that rate of fall? You'd probably get real close to your 9.8ms/s :- you'd probably have 0.1 sec to cross the bridge in a regular truck.

[rnicey]

Originally posted by 404
ok brainiacs...

assume 2 people, each having a weight tied to the end of a length of rope, swing the rope from above their heads as fast as they can, then let it slow under its own momentum. if one weight is twice as heavy as the other, which will be the last to stop...the heavy or the light one?

i'd have said the heavy one would stay rotating the longest(thinking along the lines of a car's flywheel) but i'm assured by others the heavy one would slow and stop the quickest.

Heavier one requires more of the centrifugal energy to stay up. There's a bit more too it, but basically you're lifting by swinging and therefore the greater mass requires (and consumes) more energy.

[Greg B]

To solve a problem like this requires the smarts of only one being:


Wyle E. Coyote: Super Genius

He and his ACME Catalogue would solve this problem in a snap.

[SpaceAce]

Originally posted by ryph

yes, actually
think of it when a helicopter takes off, the propeler exerts a force greater than its weight onto the ground to lift off. and in order to stay flying, must exert the same amount of force as its own weight. otherwise it will drop.

You're sort of right but you're entirely wrong. To fly, a bird or helicopter does have to exert force but that force doesn't necessarily make it to the ground, at least not all in one place. The force is distributed and diminished over area, some of it surely laterally. If your theory was true, anyone ever rescued by helicopter would have been crushed to death by the downforce of the machine over them. Every movie that ever showed a helicopter pass over a car would have resulted in a smashed car. Just think of what would happen to spectators at air shows.

There is no way that 200 kilograms of bird in flight transfer their full 200kgs to the ground beneath them. Has a bird ever flown directly over you? Probably. Did you notice extra weight? Probably not. Would you have noticed extra weight if the bird sat on your head? Probably.

SpaceAce

[SpaceAce]

Originally posted by ryph
but since this is about birds being locked inside a truck, the force has nothing else but to but directed directly onto the ground. hence the birds flying above the floor would have absolutely no impart on the weight of the car.

Assuming there are no windows. I thought of a flatbed when I read the riddle. Does it actually say enclosed? I might have missed that.

SpaceAce