The Geniuses' Thread

decisions

Thanks for that, I kept making the same mistake when squaring it.

jumpguy

jumpguy wrote: »

Hello friends, anybody up for helping young jumpguy out with a bit o' physics?

When a solid object is completely immersed in water it has an apparent weight of
16.4 N. When the object is completely immersed in alcohol, which has a relative
density of 0.825, its apparent weight is 24.8 N. Determine the volume of the object.

I keep running around with circles with this one...

8.4N more upthrust in water...

The total upthrust in water will be .825 times the upthrust in alcohol (so upthrust in water > upthrust in alcohol).

My mind is in a total fúcking spaz, with that knowledge I should be able to find what I'm looking for. I think.

Perhaps I should call it a night...seriously, any help would be appreciated. This will be annoying me forever until I solve it...

Like you said, there's 8.4 N more upthrust in water. The upthrust is equal to the weight of the fluid displaced by the body. So what's happening is that a heavier amount of water is being displaced, since water is more dense.

Alcohol having a relative density of .825 means that a given volume of alcohol will weight .825 times the same volume of water. So in our situation, the same volume of water and alcohol are displaced. That means we know that the weight of alcohol displaced is .825 times the weight of water displaced.

So let's let the weight of water be w and let the weight of alcohol be a.

a + 8.4 = w (1)
w * .825 = a (2)

Putting (2) into (1):
w * .825 + 8.4 = w
0.175 * w = 8.4
w = 8.4 / 0.175
= 48 N

Now, the volume of the object is the volume of the displaced fluid. The displaced water weighs 48N. Therefore the mass of the displaced water is 48 / 9.8 = 5 kg
(9.8 is acceleration due to gravity)

Finally, water has a density of roughly 1000kg/m^3, so the volume of the water is 5/1000 = 0.005 m^3, and that is also the volume of the object.

It's ages since you asked the question, but I hope that won't 'annoy you forever' now.

decisions

A toy, such as that shown, has a heavy hemispherical
base and its centre of gravity is located at C (Center of base in pic). When the
toy is knocked over, it always returns to the upright position. Explain why this happens.

The answer in the marking scheme is:

(toy non-vertical) c.g. has a (turning) moment about fulcrum / point of support/contact / (c.g. has) zero turning moment when toy is in vertical position

Anyone want to put this in english for me?

Thanks

SarahBeep!

decisions wrote: »

A toy, such as that shown, has a heavy hemispherical
base and its centre of gravity is located at C (Center of base in pic). When the
toy is knocked over, it always returns to the upright position. Explain why this happens.

The answer in the marking scheme is:

(toy non-vertical) c.g. has a (turning) moment about fulcrum / point of support/contact / (c.g. has) zero turning moment when toy is in vertical position

Anyone want to put this in english for me?

Thanks

Was teaching this exact question today :P

Basically, because of the hemisphere bottom, the centre of gravity acts like a fulcrum (fixed point about which something rotates) therefore the toy is totally balanced when upright due to the conservation of momentum and this is the point which the toy strives to remain at.


But tbh unless you do Applied Maths I'd stay away from Qn. 6

SarahBeep!

I need your help computer people...

Just moved back home and the internets have been changed since the last time I was here.

The new router (d-link for digiweb) has never had a password on it and I dunno how to put one on.

Helps??

jumpguy

I come with yet more physics woes, but this time of the qualitative sort... I'm trying to figure out NMR spectroscopy (boredom leads me to such places...)

I'm trying to figure out what's going on at T1 and T2*. T1 is the rate of return of the nucleus to thermal equilibrium i.e when the free induction decay curve thing becomes flat (no more emf induced). Right?

T2* is the rate of decay due to the inhomogenous field. Does that mean T1 can only be measured with a homogeneous magnetic field, and T2* only in a inhomogeneous field? In T2* the nuclei are spinning out of step due to the inhomogeneous magnetic field and causing destructive interference (in the overall magnetic flux rate change) and hence reducing the EMF produced in T2*. Correct or...?

T2 is the rate of degradation of the spin echos due to forces which are due to the nature of the material and not due to the inhomogeneous magnetic field (as that's been compensated for), right?

While writing this some ideas have become clear to me...I think, so this post has now become muddled and more in need of confirmation of correctness. Thanks in advance!

Supermensch

SarahBeep! wrote: »

I need your help computer people...

Just moved back home and the internets have been changed since the last time I was here.

The new router (d-link for digiweb) has never had a password on it and I dunno how to put one on.

Helps??

You're going to need an ethernet cable and a laptop with ethernet.

Disconnect all your computers, phones, cheese graters from the wifi (including the one you're using for the password). Then plug your computer into the router over the ethernet. There should be an ip address on the back of the router. Open up your browser and type in this ip. You may be prompted for a username and password, these details should be on the back of the router too.

The exact way of setting the password varies from router to router, You should be able to figure it out from going through the menus. If you give me the model of your router I might be able to give you better instructions

cheesefiend

Hi, smart people! I have a question. Say I wanted to create an app having next to no programming knowledge, would that be possible to do in say 8 weeks? And if I wanted to do that how would I go about teaching myself? Any advice would be greatly appreciated

Supermensch

cheesefiend wrote: »

Hi, smart people! I have a question. Say I wanted to create an app having next to no programming knowledge, would that be possible to do in say 8 weeks? And if I wanted to do that how would I go about teaching myself? Any advice would be greatly appreciated

Depends on the type of app. If it's a basic enough apply then it could be doable, but if it's something like a game, even one you might consider "simple", then probably not. I only have experience with Java and Android in regards app development, so iOS might be different.

For learning, I would advise you to check out The New Boston on YouTube. They have really good tutorials on Android app development, I think they have ones on iOS too.

If you get stuck while coding, make sure to check out Stack Overflow. Very good site, handy because people upload blocks of code you can use yourself.

cheesefiend

Supermensch wrote: »

Depends on the type of app. If it's a basic enough apply then it could be doable, but if it's something like a game, even one you might consider "simple", then probably not. I only have experience with Java and Android in regards apply development, so iOS might be different.

For learning, I would advise you to check out The New Boston on YouTube. They have really good tutorials on Android app development, I think they have ones on iOS too.

If you get stuck while coding, make sure to check out Stack Overflow. Very good site, handy because people upload blocks of code you can use yourself.

Excellent advice, thank you so much

PseudoFamous

cheesefiend wrote: »

Hi, smart people! I have a question. Say I wanted to create an app having next to no programming knowledge, would that be possible to do in say 8 weeks? And if I wanted to do that how would I go about teaching myself? Any advice would be greatly appreciated

Yeah, totally. 8 weeks is a long time, and you can have the basis of a language learnt in a few hours if you're willing to put in some hard work.

The thing with apps (and all programs) is that you're going to spend more time testing and trying to find bugs than initially programming. And once your app gets out there, you have to be able to take bug reports from the public, and fix them, especially if your app is anything but free.

Aaaaand if it's not a free app, you have to make your app stand out from the crowd graphically and feature wise, because you have to make yours better than the most popular to shift units. And then you have to add features to stay ahead.

But yeah, 8 weeks? Definitely. But once you have it out there, if you plan on it being successful, you have to keep it updated.

cheesefiend

PseudoFamous wrote: »

Yeah, totally. 8 weeks is a long time, and you can have the basis of a language learnt in a few hours if you're willing to put in some hard work.

The thing with apps (and all programs) is that you're going to spend more time testing and trying to find bugs than initially programming. And once your app gets out there, you have to be able to take bug reports from the public, and fix them, especially if your app is anything but free.

Aaaaand if it's not a free app, you have to make your app stand out from the crowd graphically and feature wise, because you have to make yours better than the most popular to shift units. And then you have to add features to stay ahead.

But yeah, 8 weeks? Definitely. But once you have it out there, if you plan on it being successful, you have to keep it updated.

I'm really not intending to sell it or it even make it public. It's for a big college project. To be honest after looking into it more it seems very scary. I'm going to give it a try but I'll probably have to come up with a back up plan. Thanks for your encouragement though

AtomicKoala

Right lads, been looking at getting a 64gb micro SD card for the last few days. The 16GB card was full before it broke, and the 8GB I'm using now is ridiculously small.

On Amazon.co.uk I've seen a few Sandisks for around £40 (€50). How are Amazon for delivering to Ireland? And should I be wary of anything with regards to the cards themselves? (I do know it will work in my phone, and I can easily format it to FAT32).

Thanks!

johnmcdnl

AtomicKoala wrote: »

Right lads, been looking at getting a 64gb micro SD card for the last few days. The 16GB card was full before it broke, and the 8GB I'm using now is ridiculously small.

On Amazon.co.uk I've seen a few Sandisks for around £40 (€50). How are Amazon for delivering to Ireland? And should I be wary of anything with regards to the cards themselves? (I do know it will work in my phone, and I can easily format it to FAT32).

Thanks!

Never had a problem getting stuff from Amazon but they don't deliver some stuff to Ireland. 3-4 days is the most I've ever been left waiting on anything from them. If they say they won't deliver to Ireland check out Parcel Motel (there's a huge thread about them over in the Bargain Alerts section), great service.
Basically you give Parcel Motel's address in Belfast and they put it in a locker near to your home for you to pick up when you get a chance. Worth a look especially if your based in Dublin as most of the lockers are located in Dublin at the moment.

As for the card themselves - as your buying from Amazon you should be good as Amazon are a very reputable company, if your were buying a cheap SanDisk off eBay or something I'd be a bit wary that it might be a dud card especially if it was coming from China or SE Asia.

Lawliet

Got a stats exam tomorrow, the guy teaching the course is useless, a lot of his past exam questions are things he's never explained,
Does anyone know what a parametric variable is? I can't seem to find a definition for it anywhere. Also what are confidence intervals?

Jamie Starr

Lawliet wrote: »

Also what are confidence intervals?

Example:

First interval: "Hmm, this exam might not be too difficult after all."

Second interval: "Yes! I think this is going to go well!"

Third interval: "CRAP CRAP CRAP CRAP CRAP CRAP CRAP."