/sci/ - Science & Math

[Problems !xi8/JKFwzo No.4792027]

This board is full of failures and I will prove it.

Solve these three very simple problems, /sci/, and you will get the respect of realy /sci/entists.

>Problem #1

You have a falling ball that bounces and comes back up. Draw the resultant force vector at each time step (from the ball). You must draw the vector such that you get the magnitude and direction correctly for each.

[Problems !xi8/JKFwzo No.4792035]

>Problem #2

This is a typical oscillating pendulum. Draw the vector of acceleration at each time step. Again you must draw the vector such that you get the magnitude and direction correctly.

[Anonymous No.4792039]

Going down: force downwards
At the bottom: force upwards
Going up: Force downwards

[Problems !xi8/JKFwzo No.4792044]

>Problem #3

On the same inclined plane, which one will roll faster, a solid disk or a ring of the same radius?

[Problems !xi8/JKFwzo No.4792047]

>>4792039
>WRONG
draw them with direction and magnitude you imbecile

[Anonymous No.4792053]

>>4792044
They roll the same, nerd.

[Anonymous No.4792050]

>only physics questions

[Anonymous No.4792051]

>>4792027
>>4792035
>>4792044
wow, the homework fags are getting smarter in their ways of getting us to help them. gj.

>>4792039
god dammit you proved him right, you know nothing. at the bottom there is a force upwards and force downwards. gravity is always acting. there is also wind resistance in the opposite direction that it is moving.

[Anonymous No.4792052]

>>4792035
Is the string taut and massless? Can I assume this oscillation is linear and use the relevant 2nd-order ODE? Is this happening on Earth or is their generally a constant "downwards force?"

[Anonymous No.4792054]

>>4792044
This a basic rotational motion question.


I just forgot my iotas.

[Anonymous No.4792055]

This is highschool level stuff.

If nobody answers this properly, it's because nobody can be bothered to answer highschool level stuff.

Sage. Please don't solve this kid's homework. You're not proving anything to anyone, you're just helping a real shithead of a kid with his boring homework.

[Anonymous No.4792056]

>>4792051
I'm not that guy but he asked for the net force. I want to know if the ball is implied to be bouncing or not. If so, then to come back up an upwards force would have to accelerate it to move up and he would be right.

[Problems !xi8/JKFwzo No.4792057]

>>4792052
You can assume that the string is massless. After that you're on your own.

and also
>>4792051
>WRONG
draw them with direction and magnitude (obviously relative magnitude, I didnt give you any values)

[Anonymous No.4792058]

>>4792044
I assume the solid disk because it has more weight to counter the air resistance?

the other two are ridiculously easy so I won't even bother

[Anonymous No.4792061]

>>4792051
>at the bottom there is a force upwards and force downwards. gravity is always acting
>Draw the resultant force vector at each time step

[Anonymous No.4792063]

>>4792051
He said RESULTANT force. The wind resistance and the weight sum up to a RESULTANT force going downwards. At the bottom the force down and the force up sum up to a RESULTANT force going up. Going up they sum up to a RESULTANT force going down.

>>4792044
>they roll the same
>he thinks their moments of inertia are equal

[Problems !xi8/JKFwzo No.4792065]

>>4792055
Why don't you look at all the retarded answers that are being posted and then tell me that "they can't be bothered"

You can't solve this. And it shows.

[Anonymous No.4792069]

>>4792057
lol you can fuck right off retard. do you own homework. do you really expect your lame attempt to get us to do your homework by offering us 'respect' to work? for gods sake, this is high school stuff, any average hs grad should be able to do this

[Anonymous No.4792070]

>>4792044
Does this problem include friction or not? Do the two objects have the same density or the same mass?

>calling other people failures

[Anonymous No.4792071]

>>4792044
Rolling is about where the kinetic energy is going. All of the gravitational energy is being converted to translational and rotational kinetic energy. Assuming that you mean the second thing is a thin hoop then you can do some algebra to find which one has the most translational velocity.

[Problems !xi8/JKFwzo No.4792067]

>>4792053
>WRONG

This board is just fucking retarded...

[Problems !xi8/JKFwzo No.4792076]

>>4792063
>>4792056
>WRONG
You MUST draw the resultant force vector. Otherwise you're saying nothing.

This board is much much dumber than I thought

[Anonymous No.4792072]

>>4792067
Their centers of mass are the same. Just treat them as a point mass and they roll at the same speed retard

[Anonymous No.4792074]

>>4792065

That's what I mean, kid, anyone who can actually do it can't be bothered. You're getting other highschoolers to do your highschool homework. I'm not stupid enough to be goaded into doing it for you.

If a child came up to you and sat there frothing at the mouth telling you you can't solve 5+x = 10, you wouldn't really pay much attention, now, would you?

I really feel sad that anyone's actually even trying to help you with your shitty attitude. At least some people on this board have the honesty to just call it homework rather than trying this "subtle" approach that anyone who isn't mentally retarded can see through.

[Anonymous No.4792079]

Force is downwards always. Gravity.

[Anonymous No.4792080]

>>4792044
I loled I remember this from highschool.

It's the ring. Rotational Inertia mah nigga

[Scientist !!ThFjnJh4EkH No.4792077]

>>4792027
>This board is full of failures and I will prove it.
So, not recalling basic high school physics makes you a retard. K.

Do you remember all of your history, or chemistry? Are you polymath enough to take your arrogance to the logical conclusion? F off asshat.

[Problems !xi8/JKFwzo No.4792078]

>>4792058
>WRONG
You fucking moron
>implying heavier objects fall faster

This board... for fuck sakes...

[Problems !xi8/JKFwzo No.4792083]

>>4792061
>WRONG
Draw the vector so you can tell both direction and magnitude

[Anonymous No.4792085]

OP is happy he passed 1st year Newtonian Physics course, and now he seeks to rule with an iron fist over /sci/

[Anonymous No.4792086]

>>4792078
>this post
>holy shit he actually thinks this anything to do with the post he quoted

[Scientist !!ThFjnJh4EkH No.4792087]

Also:
Problem 1:
When not in contact with the ground, under the Newtonian physics model, a constant force downwards on the ball. When the ball touches the ground, it begins to contract, and over time the upwards force on the ball increases, until it becomes bigger in magnitude than the gravity force, and the net force is upwards. After a time, while still in contact with the ground, after its velocity has changed upwards, the "impact" force decreases, until it's eventually less than gravity, and disappears entirely as the ball leaves contact with the ground.

[Anonymous No.4792084]

Just hand this in

[Anonymous No.4792089]

>>4792087
Unfortunately, he asked us for the force upwards at that instant it hit the ground. It would be equal then, da?

[Anonymous No.4792090]

>>4792078
heavier objects with the same surface shape do fall faster retard. they are able to counter air resistance better. jesus, you must be the retard of the class

[Problems !xi8/JKFwzo No.4792093]

>>4792070
>WRONG
Just for asking that question. Please tell me how things can "roll" without friction. Fucking moron

>>4792071
>WRONG
Talking about the problem does not equal solving it. Fucking science fanboy. You don't know.

>>4792072
>WRONG
You idiot... there are no words... Are they in free fall??

>>4792079
>WRONG
Please die. Just... please.... is it moving downwards??? FFS

[Scientist !!ThFjnJh4EkH No.4792091]

Problem 2:
Constant force downwards from Newtonian gravity. There is a tension force from the robe acting on the "ball" too. I actually don't recall this problem that clearly - it's been quite a while. Should be pretty straightforward to solve. It's basic calculus.

I suspect that the acceleration is a net zero at the bottom of the arc, going to its largest magnitude at either end, and the acceleration vectors point towards the "middle" perpendicular to the angle of the rope.

[Scientist !!ThFjnJh4EkH No.4792096]

>>4792089
The instant it makes contact with the ground? Then the "contact" force is stupidly small at that moment, approaching zero, and the net force on the ball is about gravity. Only a little after contact will the upwards "contact" or "normal" force have a greater magnitude than the gravity force.

[Problems !xi8/JKFwzo No.4792098]

>>4792084
>WRONG
Wrong magnitudes and directions

[Anonymous No.4792095]

Everybody calm the fuck down. I got this!

[Anonymous No.4792102]

>>4792091

Please don't answer him. Delete those posts if you would, you're really only encouraging him.

As long as retards can get their homework answered by posting on /sci/, they will keep posting homework on /sci/. Don't encourage them.

[Anonymous No.4792103]

>>4792027
>Problem #1

Only force is gravity initially. The force is directed downward and it's magnitude is determined by F=mg.

The force present when the ball hits the ground is the normal force which exerts an upward force on the ball.

Final force is gravity pulling down again. While the ball has velocity and is traveling upward it's decelerating due to gravity and will eventually stop and start accelerating in the opposite direction (towards the ground).

Fuck you I'm not giving you any diagrams. It's 4:30am and I don't feel like fucking around in paint.

[Anonymous No.4792099]

>>4792095
>no magnitudes
>force upwards on the ground

JESUS CHRIST YOU'RE WRONG THE BALL ISN'T COMPRESSED

[Anonymous No.4792100]

>>4792093
>implying they will not roll the same if there is no friction
>implying the density and/or mass of the objects does not matter

Looks like you're the retarded one, son.

[Anonymous No.4792104]

>>4792098
Are you shitting me I spent 4 hours on that drawing

[Anonymous No.4792105]

>this thread

[Scientist !!ThFjnJh4EkH No.4792106]

Problem 3
Uggg. This is a moment of rotation problem. I didn't really do many of these.

Let's see if I can reason my way through it.

The two disks will both reach the ground. The difference in gravitational potential energy is the same. They will have differing amounts of rotational energy and linear kinetic energy. The difference has to do with the different ratios of the rotational moment to the mass. Ugg. Sorry, I can't be arsed to actually write down the math to figure this out for sure.

Let's see... the hollow disk will have a greater rotational moment of inertia than a solid disk of the same mass. Thus, I suspect that it takes more energy to get the hollow one rolling, and thus I suspect the solid one reaches the ground first. Sue me if I'm wrong.

[Anonymous No.4792110]

>>4792099

>YOU'RE WRONG THE BALL ISN'T COMPRESSED

Sorry my bad. I am resubmitting it as .jpg.

[Anonymous No.4792107]

>>4792106
My lawyer will be calling you shortly.

[Problems !xi8/JKFwzo No.4792112]

>>4792087
>WRONG
What are the magnitudes of the forces? Twice as much? 10 times as much? At least give me an order of magnitude.>>4792090


>>4792091
>WRONG
Draw it. Direction and magnitude.

>>4792095
>WRONG
You fucked up the magnitudes.

>>4792096
>WRONG
Be quantitative. Bigger by how much?

[Anonymous No.4792113]

>>4792110
10/10

[Anonymous No.4792111]

>>4792027
I assume you want all the force vectors? Including drag/air resistance

1.In which case a large one going down in the first one, with a small one going up(wind resistance/drag)

2.A force also pointing up from the ground(normal force) and a another force equal to the normal force pointing down(Newton's third law,whatever the mass is times 9.81)

3.Gravity arrow pointing down equal to the first pic. Another drag arrow down, slightly less than first pic.

Not 100% sure if the drag is equal in part 1 and 3. Not an AE so it's not my specialty.

[Anonymous No.4792114]

>>4792110
I love you.

[Scientist !!ThFjnJh4EkH No.4792116]

>>4792112
[problem 1]
>What are the magnitudes of the forces? Twice as much? 10 times as much? At least give me an order of magnitude.
>Be quantitative. Bigger by how much?
It depends on the composition of the ball and the composition of the ground, the relative speeds, and so on. If we were to model this as an impulse aka ala a dirac function, then the "contact" force is infinitely bigger than the gravity force and works over 0 time. In the real world, it depends.

[Problems !xi8/JKFwzo No.4792115]

>>4792100
>WRONG
lrn2physics
Go read som scifi you imbecile

[Problems !xi8/JKFwzo No.4792119]

>>4792103
>WRONG
Wrong magnitudes

>>4792106
>CORRECT
Finally!! That's only one down. Someone had already given a correct answer before but didnt put a justification so i ignored it. This >>4792080

[Anonymous No.4792121]

>>4792115
>butthurt about thinking that all objects fall the same under gravity in all situations
>butthurt about thinking that mass and density of rolling objects doesn't matter
>butthurt that somebody deigned to not fall into the trap of assuming friction when it was not mentioned

[Anonymous No.4792120]

>>4792119
I didn't give you any magnitudes and I have my directions right.

[Scientist !!ThFjnJh4EkH No.4792123]

>>4792121
To be fair, he said "roll", and it will roll only if there's friction or if it was originally rolling. The standard interpretation is that they are originally at rest. You are the butthurt.

Now, I have no problems with clarifications and such. That's to be commended.

[Problems !xi8/JKFwzo No.4792124]

>>4792111
>WRONG
Only resultant forces. So one vector for each ball. Idiot.

>>4792116
>CORRECT
Well at least you have the reasoning right. The force upward is, in the real world, on the order of 10^3 times larger than F=mg. You can think of it like this: How many rocks do i have to place on my hand to feel the same force as a single rock dropped on my hand from a given height?

Now we only have the pendulum problem left. This one is tricky. There is no solution without a drawing for this one.

[Anonymous No.4792127]

Chemistry time!

A sample of a pure, gaseous hydrocarbon is introduced into a previously evacuated rigid 1.00 L vessel. The pressure of the gas is 0.200 atm at a temperature of 127°C. O2(g) is introduced into the same vessel containing the hydrocarbon. After the addition of the O2(g), the total pressure of the gas mixture in the vessel is 1.40 atm at 127°C. The mixture of the hydrocarbon and oxygen is sparked so that a complete combustion reaction occurs, producing CO2(g) and H2O(g). The partial pressures of these gases at 127°C are 0.600 atm for CO2(g) and 0.800 atm for H2O(g). There is O2(g) remaining in the container after the reaction is complete.


Write the balanced chemical equation for the combustion reaction and determine the formula of the hydrocarbon.


It's off the most recent AP Chem exam.

[Problems !xi8/JKFwzo No.4792130]

>>4792127
Number crunching is for idiots.

Science is about intuition about the physical world. Come up with some chemistry problems that you can solve purely by intuition and we can make this thread multidisciplinary.

[Anonymous No.4792134]

>>4792127

>chemistry
>a hard science

[Problems !xi8/JKFwzo No.4792133]

>>4792091
Didn't read the last part of this post.
>WRONG
It isn't

[Anonymous No.4792136]

>>4792124
>Only resultant forces. So one vector for each ball. Idiot.
Welp didn't read that.

In which case eliminate the following:

1. Any mention of drag.

2. All gravity based force vectors are slightly less than 9.81(again I'll assume that their is a drag force)

3. Get rid of the reaction force heading downward I mentioned in step 2.

That should have that one correct/fixed.

[Anonymous No.4792135]

>>4792127
CH3P(O)F2 + (CH3)2CHOH → [(CH3)2CHO]CH3P(O)F + HF

[Scientist !!ThFjnJh4EkH No.4792138]

>>4792133
Meh.

[Problems !xi8/JKFwzo No.4792140]

>>4792136
>WRONG
And you're also an idiot for not realizing that someone already solved that problem.

The only remaining problem is the pendulum one.

[Anonymous No.4792145]

>>4792123
He said
>which one will roll faster
If there is no friction, then they roll the same. I suspected a trick question, and had I not raised this point I've no doubt he'd be shouting about how retarded everyone is for not realizing.

[Scientist !!ThFjnJh4EkH No.4792148]

>>4792145
Meh. True. He is a complete asshat.

[Problems !xi8/JKFwzo No.4792153]

>>4792145
This isn't fucking middle school. Life doesn't have trick questions. Just answer the problem at hand. You were just trying to argue the question in order not to answer it.

If there was no friction, they wouldn't roll. They would slide. Now go read some more Michio Kaku. It's making you really smart.

[Problems !xi8/JKFwzo No.4792158]

Well, since /sci/ is incapable of answering all 3 of these extremely simple and intuitive problems, you are all deemed complete and total failures at science.

Enjoy your reading about black holes and quantum mechanics from books with no equations. You will never be capable of understanding anything about these fields. Just leave these to the people who know what they're doing. Thanks.

Goodnight!

[Anonymous No.4792159]

>>4792153
>Life doesn't have trick questions
Sounds like somebody is aged 18 or under.

>You were just trying to argue the question in order not to answer it.
You still haven't specified the mass or density of the objects, as if these aspects are not fundamental to the problem. Possibly because you don't understand it yourself.

[Scientist !!ThFjnJh4EkH No.4792166]

>>4792158
He's leaving now? Excellent. I guess I should have not posted at all.

[Problems !xi8/JKFwzo No.4792167]

>>4792159
>ffs
You fucking moron. It doesn't matter. Try rolling a dumbell that you use to do weights down an inclined plane versus an empty soda can. You're a moron.

[Anonymous No.4792172]

>>4792158
>Enjoy your reading about black holes and quantum mechanics from books with no equations. You will never be capable of understanding anything about these fields.

Projecting.

[Problems !xi8/JKFwzo No.4792173]

>>4792166
Well do you have an answer?

Because it's pretty damn clear that you were the only one with any physical intuition here. Everyone else is just a liberal arts major that likes to read about string theory.

[Problems !xi8/JKFwzo No.4792181]

Didn't think so. Goodnight failures. Might wanna go back and get that GED!

[Anonymous No.4792195]

haha people are actually responding to this thread. this is fucking funny

[Anonymous No.4792196]

>>4792181
>Google GED
>Gedling Borough Council

[Anonymous No.4792205]

>>4792167
>He didn't actually work the problem through by himself

[Anonymous No.4792210]

your all morons and im gonna prove it
>scans irrelevant high school problems and posts it on the internet
there, lets see if you can solve my homework i did last night
>arms crossing smug look on face

heh, maybe i should test /lit/ by having them write my great gatsby essay that's due next friday

[Anonymous No.4792228]

>>4792027
hey, how about you do my homework for once, highschoolfag?

[Ruski !ir4b7Vrums No.4792232]

>>4792228
7.

[Anonymous No.4792230]

>>4792228
Mechanical engineer?

[Anonymous No.4792235]

>>4792230
>every engineer
not mechanical

[Anonymous No.4792234]

>>4792228

fucking gyrospcopes how do they work?!

[Anonymous No.4792303]

Done.

[Anonymous No.4792310]

>>4792303
>No force since it's free fall

>I hope I don't have to explain that.

>The ring will roll faster...

Stopped reading right there I couldn't believe it took me that long to realize you were trolling 10/10

[Anonymous No.4792331]

>>4792110
easily the best post in the thread

[Bernkastel !!8eF6CGNIpsC No.4792340]

>>4792303
>ring is lighter
>will fall faster
oh BOY

[Anonymous No.4792343]

Here are the correct answers. I'm curious to see what OP will say.

[Anonymous No.4792369]

>>4792340
>>4792310

>implying that guy was serious at all

Goddamn you people are morans

[Anonymous No.4792371]

>>4792369
0/10 at least you tried son

[Anonymous No.4792373]

>>4792100
If there is no friction, neither the disk nor the ring will roll, as they will slide. They have no initial rotational momentum, and there is no force changing this.
tl;dr without friction, balls don't roll but slide

[Anonymous No.4792402]

>>4792303
>ring is lighter
>will fall faster

inb4 Galileo

[Anonymous No.4792424]

>>4792303

[Anonymous No.4792484]

Can we make this into a Dunning-Kruger thread?

http://www.youtube.com/watch?v=eVtCO84MDj8

[Anonymous No.4792514]

>>4792027
hey faggot. if you cant do simple problems such as these, then you should probably drop out of the physics class in which these problems were assigned as homework. your dream of becoming a physicist and trying to be smart is dead, because you are in fact a retarded faggot

tl,dr - OP is a stupid faggot and always will be

[Anonymous No.4792524]

>>4792102

it's a stupid thread but it's obviously not a homework thread. the most you can say is that op is some highschool brat who thinks he knows something.

in which case, he'll fit right in, judging by the amount of retarded answers. in fact the only intelligible posts here are by a singular tripfag. hopefully all the smart people just aren't posting, or /sci/ is a real cesspool.

[Anonymous No.4792548]

source: 2 years of engineering undergrad. also its juts kinda obvious.

[Anonymous No.4792554]

>>4792548
can't tell if troll or retard

[Anonymous No.4792625]

Why are so many people so committed to defending the honor of this board and ALL it's members especially when they don't even know how many idiots regularly use this board?

There's a saying that comes to mind; I'll adapt it to the present context: "99% of /sci/ gives the other 1% a bad name". Then again, the idiots might only be the most vocal even though they're the minority because they 'somehow' have more time to spend here making stupid comments all-day, everyday.

Then again all this pretentiousness could just be recursive role playing brought on by troll adaption. It's just if that's the case, it comes across as being so fucking forced.

Anyways, if this was a really a homework question then OP would have gotten the correct answer with the first 5 posts. Seriously, when have you NOT seen a homework question get answered here?