Wat wud happen?
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Wat wud happen?
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a. the velocity would be 4000 km/h
b. the bullet would fall at a velocity of 9.81 straight down
c. trains dont go that fast
d. need mph to understand properly
e. it would go back in time and kill ur father.
Should have made a poll. Darn.
haha
Physics was never my strong suit but it is not hard either.
The bullet (along with the train, gun and stick figure man) has enough energy applied so all of them are moving right (in your drawing) at 2000kmh. The direction (right) and the speed (2000kmh) together we call the velocity of the bullet, train, gun, and stick man.
When the gun fires, enough energy is released to cause the bullet to change it's velocity (it's direction, speed, or some combination of).. In this case to move in a new direction, left in the drawing, at a new speed, relative to the stick man.
So from the stick figure guys PoV nothing special happens - it's just like any other bullet leaving a gun. It appears to travel off the left at 2000kmh from his point of view.
But if you were an observer on the ground watching this all happen... it would appear the train is passing you at 2000kmh headed right, and the bullet would just drop to the ground as if it had 0 left-right velocity, and gravity imparted a downward velocity.
The fact that we live on a world with air complicates it a bit; air, even though we can't see it has weight, energy, which we feel as wind. It adds in a drag factor which throws things off but that is roughly the way it works.
It's called frame of reference. Basically the reason you can drink a cup of coffee in your moving car. Or in an airplane at 600mph and since your coffee moves with you at the same speed, from your PoV it is standing still. A little bit of vector math can be used to explain how to add velocities in technical terms but we all understand it intuitively too because we experience relative velocities daily.
I promise not to look down on you if you can laugh at lawyer jokes.- minnow



holy shit. physics 1 is the class that killed me too.
^^^
I just read a book by a mathematician (and teacher) named Keith Devlin. Basically he has some interesting theories on why it is possible for all of us to learn various types of math if we must, but the majority of us really struggle with it (my self included). It's not just you. It is pretty much all of us.
I promise not to look down on you if you can laugh at lawyer jokes.- minnow




I have never taken a physics class, but I don't think this is right. The bullet and the man are at rest. When the gun is fired the bullet will leave the muzzle at 2000 km/h. To the man moving away from the point of firing, the perceived velocity will be 4000km/h.
If the bullet fell straight down, then if you turned and fired the opposite direction, would it refuse to come out of the gun? No, of course not.
If I was standing beside the tracks and you are on the flatcar and we both fire when you reach the point I'm standing, would your bullet fall to the ground while mine traveled toward a the target?
I don't think the speed of the train matters, much like the fact the earth is spinning at 66,000 mph while I type this.
But like I said, I really don't know nuttin about physics or it's laws. I'm just subject to them.





the answer to this practical impossibility example is b.
Nah, the bullet, the gun and man are not at rest. They have the same velocity as the train. The are at rest only relative to each other, but not someone else on the ground.
It's simple really if you think about it differently. If a car passes you at 60 mph while you stand on the street, the car, the person in the car, and the cup of coffee they are drinking are all going to wiz past you at 60mph.
If someone in the car tosses the cup of coffee behind their head at 5mph, from their PoV in the car, the cup will be moving 5mph away from them, and from your PoV on the ground it will appear as if the car and driver are still passing you at 60mph, while the cup in the car only at 55 mph.
The bullet only would appear to fall straight down from the PoV of someone standing in a train station watching as the train passed. Imagine you standing there... watching that... over a few moments... the bullet falling, the train further and further away from the bullet (and you). Now imagine it from the PoV of the guy on the train. All he sees is the bullet falling (like any bullet will once fired) and the bullet apparently traveling away from him at the bullet's exit speed of 2000kph.
It is a bit confusing too because of something non-intuitive but we all learned it. If you fire a gun (or throw something) parallel to the ground, no matter how fast it travels away from us, it falls at the same rate, the speed of gravity (it can be confusing though as some things "fly" too which means they have lift while traveling through the air, but bullets don't).
So ... imagine that car again.... now toss the cup of coffee behind your head out the rear window at 60mph... from your PoV in the car it will appear to be moving away from you (behind you) at 60mph, and falling at the speed of gravity. From the PoV of someone on the street, they see yu and the car pass at 60mph... and a cup... (now with a velocity equal to yours on the street) falling down.
I guess the last way to think about it is with vectors, like you would in school. Imagine an arrow where the length of the arrow is the speed of a thing, and the direction is, well its direction.
---- 2000kph ---> (this is the original velocity of the bullet).
to figure out it's new velocity, you have to learn how to add vectors but in this case it is easy:
Add the vector imparted to the bullet by the gunpowder and gun:
<---- 2000kph --- (this is speed and direction imparted when the gun fires)
When you add those you end up with vector of 0 direction and 0 length* (sort of, see below).
But there is another force at play.. the gravity. When the bullet was in the gun, in the hands of the man, on the train, the rigid structures of them held the bullet above the earth. When the bullet left the gun that was no longer true and it falls.
*In reality that is not true either. Both the observer on the platform, and the train, and the man on the train, and the gun, and the bullet also have velocities imparted by the spin of the earth, the movement of the earth around the sun, our solar system in the galaxy, and so on. Fortunately we can ignore the velocities we have in common and only care about the differences.
This is a difficult concept in physics, that we don't have absolute velocities, only relative ones. That there is no place in the universe where we can say that is the point at which everything is at rest and not moving. There is no such place. So you can see the bullet exiting the gun as a 2000kph acceleration in a different direction then the train, or as a sudden 2000kph deceleration - your choice, whichever is convienent depending on your frame of reference.
I promise not to look down on you if you can laugh at lawyer jokes.- minnow
M is correct, though b is misleading too because it is not clear that the observer is someone on the ground (vs the guy on the train).
It just that it only appears to fall straight down to someone who is at rest relative to the train. To the stick man on the train it looks just like any other bullet exiting a gun from any other frame of reference.
If you don't believe it, go into your house (close the windows if it helps you see why) and try throwing a ball using your normal strength. How fast does it move away from you? Whatever, 10mph?
Now try the very same thing inside of an airplane moving at 600mph. I bet everyone here already knows that the ball does not appear to move away from you any faster (or slower) then it did inside of the house.
But ask someone down on the ground what they see and you'll get a very different story.
I promise not to look down on you if you can laugh at lawyer jokes.- minnow






It seems like everyone here let physics get in the way of the important question -- the one at the end of your post:
"What would happen if Ernie does not stop staring at your cameltoe?"
It would be entirely up to you. You could have the bouncer throw him out. Or you could realize he is completely under your spell and take advantage of it. You could look down at yourself, and then at him, lick your lips seductively and suggest you go to the VIP room. There you could empty his wallet and send him on his way.
If I'm ever in your club, you could try it on me and see how it works.![]()
I see no reason to insult him. I've read matters about human experiences (which we should be able to grasp if people just try to step into another person's shoes) that seemed far more absurd to me.
We simply aren't wired to understand much of physics intuitively. If we were there wouldn't be any need for the rigid courses and strict thinking physicists hold each other too. No need for puzzle questions like this one to make us think. In fact I think a big reason why people give up on math and physics (well science) is the ridicule they receive even by teachers.
While I have met people with rare gifts (e.g., to sing, to understand math), our brains evolved to deal with finding food for our bodies, attracting mates, social relationships, to deal with relatively slow moving animals, etc. We are just not pre-disposed to grasp the types of problems physicists spend their time getting their heads around. He should get credit for trying to ask what would happen? Curiosity is the most important pre-requisite any physics student can have.
I promise not to look down on you if you can laugh at lawyer jokes.- minnow





Turn that stick man around facing into the wind on that uber-supersonic train (staple his feet down of course). Then have him aim slightly upwards and fire that damn gun.
1.) Does the bullet even leave the barrel?
2.) If so, does it go out and up a bit then hit him in the face?
3.) If so, how fast does the gray matter spray backwards?
4.) If I am running behind the train (also at an impossible speed) filming this event, do I get splattered or does the debris just disintegrate as it hits me?
5.) Should I not wear a hat to this event?
These are the REAL questions to be asked!
Mythbusters needs to try some of this shit instead of blowing up watermelons.
When life gives you lemons, make lemonade... then find someone whose life gave them vodka, and have a party.




You have a tendency of dramatizing a subject. In this case, what is clearly an issue of common sense, you are converting it into an issue of physics. You do not need to be a physicist to answer the question asked by lucky one. All you needed to know was some basic stuff.
It did not even require the knowledge of simple formula like: v = gt, v = √(2gx), x = gt2/2, etc.
It was a straightforward common sense question but I can always count on you to sensationalize a topic.




"Peter, did you take Stewie to a strip-club? He smells like sweat and fear." - Lois and Stewie (Family Guy) ... "Through early morning fog I see, Visions of the things to be, The pains that are withheld for me, I realize and I can see..."
I promise not to look down on you if you can laugh at lawyer jokes.- minnow









LOL!
Margarita Villian - If the gun were fired the other way, it would have a forward velocity of 4000 km/h referenced to a stationary bystander, and a velocity of 2000 km/h relative to the guy on the train shooting it. The train was kind enough to provide the initial acceleration for teh first 2000 km/h of the bullets velocity, along with everything else in it. This is why fighter planes don't run into their own bullets (though for other reasons, firing a gun at supersonic speeds does present issues).
This is all negating other factors like increased drag on the bullet at the higher speed, air compression in the guns barrel, and so on.
I love physics. It's the best stuff ever. Can we move on to gravity/time/space now? PLEASE??!!![]()




You are WRONG.
Margarita Villain is saying following:
Then have him aim slightly upwards and fire that damn gun.
... which means Law of Parallelogram Of Forces (which also applies to velocities) will come into play and the resultant velocity of the bullet will depend on the angle at which the gun is fired.
I think you need to read a little less from Dawkins and a bit more from classical mechanics. What do you say hombre?





Cyril, you are picking this apart to an amazing degree of retardedness.
MargaritaVillain - at what angle - PRECISELY - was the gun pointed upwards? Was it in fact pointed DIRECTLY forward, or was it slightly to one side of the other? Was it in fact aimed upwards or to one side at all in relation to the axis of the train, or just in relation to the guys standing on it - maybe the gun was level relative to the trains axis, but the guy was leaning forward into the wind so it was slightly up to him? What oif - dear God - the trai was going around a gentle CURVE whe all this happened - does anyone know? What was the radius of said curve? Was it constant? Did the train mintain steady velocity whilst negotiating it? nd was the train even LEVEL?! What of ot was goping up hill or downhill! Now we're back to whether or not the gun was paralell to what axis! Did this happen at the same instant that a tectonic plate let go like the one that caused the tsunami, alterning teh earths rotational speed right at that moment? Were there any solar flares? here was the moon? Comets? ARE YOU SURE?!?! I also am going to require information about barometric pressure, humidity, particulate pollution, wind speed, and a few things about the gun, too. Is the bullet full metal jacket or hollow point? What caliber? Was it cleaned recently? Was the round fired lubricated at all, teflon coated perhaps? Definitely going to need to know the manufacturer so we can determine the barrel twists and therefor the likely level of gyroscopic forces at play on the bullet itself as it rotates. Also the altitude the train was at when the bullet was fired...
Inquiring Cyril's want to know. :rolleyes:
BUT -
OH SHIT! ALL of this requires that we know the EXACT postition of the train, the gun, the bullet, the bystanders and everything else - BUT WE ALREADY KNOW THEIR VELOCITY!!!! This is TERRIBLE NEWS! DO you KNOW what that MEANS?!?! Thanks to the unertainty principle, WE'LL NEVER FUCKING KNOW!!! All we can do is approximate to a finer and finer degree - but because we MEASURED these things THEY FUCKING CHANGED and we won't know how much antil we measure them AGAIN which will make them change AGAIN!!! DAMNIT!!!
Okay I'm done now...![]()
Actually I was responding to AJs post and he was correct in giving a simplified example that was the opposite of the original posting; he was making a simplification which is helpful in reinforcing in the spirit of the original puzzle. MJ was trying to be humorous of course and suggesting if the gun is lifted slightly would the bullet blow back in the stickman's face (no of course).
You are also correct that if it is aimed in a slightly different direction then that it will effect the velocity from the PoV of a stationary observer who could add up the velocity of the train with the exit velocity of the bullet to calculate the observers apparent velocity.
However again... from the PoV of the guy on the train. For the guy on the train he feels as if he is not moving (sans wind in his face that give him hints that he is), and it is the earth moving below him. As long as he is at a constant speed on the train (not accelerating), and except for some hints that come from air resistance and gravity, he basically feels like the train is at rest. From his PoV....
If gunpower explodes with enough force to cause the bullet to have a change in velocity of 2000kph relative to the stickman, then that is its exit velocity from the PoV of the guy on the train. It doesn't matter to him which way the gun is pointing, from his PoV the bullet exits at a speed of 2000kph away from him. After that additional forces get involved (air resistance, gravity, of course).
What makes the original puzzle interesting is that it causes us to think about how different observers view the same event relative to themselves
So yes you are correct but also seemed not to grasp that AJ was not trying to provide an exact reply to MV, but a simplified one to clarify a basic point of how things work.
I promise not to look down on you if you can laugh at lawyer jokes.- minnow





HOLY SHIT
way to take the fun out of a decent thread guys.
You didn't just kill it, you obliterated the damn thing!
btw...the Bert picture was clearly the best part of all this
When life gives you lemons, make lemonade... then find someone whose life gave them vodka, and have a party.
^In that case I will be posting it randomly and sporadically as I feel necessary.
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