[Feynman]

I receive a lot of PMs regarding math/physics questions, so I've decided to open up a help desk to further assist the community. [/align]

My qualifications:

• I have a BSc.Hons. in Physics
  


• I run undergraduate help sessions in school
  


• I have hundreds of hours in lab experience
  


• I have been a TA for three semesters in a row
  

What I can help with:

• Algebra and trigonometry
  


• Linear Algebra
  


• Precalculus
  


• Multivariable differential and integral calculus
  


• Vector calculus
  


• Ordinary and partial differential equations
  


• Kinematics
  


• Classical mechanics
  


• Electromagnetic theory
  


• Quantum mechanics
  


• Optics
  


• Thermodynamics and statistical mechanics
  


• Fluid dynamics and introductory oceanography
  


• Some basic group theory and Lie algebra(physics-related only)
  


• Some electric circuits
  


• Special and basic general relativity
  


• Basic nuclear physics
  


• Biophysics
  


• Particle physics and cosmology
  


• Lab reports, research papers, and honours theses
  


• Math/physics career/university advice
  

What I cannot help with:

• Computer science
  


• Pure math (including writing proofs)
  


• Real/complex analysis
  

My rules/Conditions:
I'm extremely approachable, and I will assist you until you feel comfortable with what you're doing.
I do not offer homework help.
Please be patient. This is a free service, and I'm taking time out of my own day to help.
You can also PM me questions.
If you choose to help another user, please PM them instead of posting here.
I provide full, written solutions to problems. If you don't like my notation/writing, sucks. Change it how you see fit. If I'm lazy, or don't have paper, I'll type out solutions.
There are many different methods to solve problems. If it requires a certain method, let me know!

[Kosmos]

I can vouch for Feynman. He is fantastic at what he does and I can assure you that he will help you with any question you may have.

[Reνolution]

This is an awesome service you are providing here. I can vouch for this as Feynman has saved my ass so many times on Physics assignments :P

[Neal Caffrey]

Having a bit of trouble regarding connected masses hanging on a pulley.
I'm pretty shit at the whole topic of Motion, so some help would be appreciated.

A 12kg mass is held on a smooth surface and is connected by a string and pulley to a 2.5kg mass which dangles in mid air. If the 12kg mass is 5 m from the end of the surface;
a) maximum speed does it reach before crashing to into the pulley?
b) How much time does it take for it to crash into the pulley?

[Feynman]

Having a bit of trouble regarding connected masses hanging on a pulley.
I'm pretty shit at the whole topic of Motion, so some help would be appreciated.

A 12kg mass is held on a smooth surface and is connected by a string and pulley to a 2.5kg mass which dangles in mid air. If the 12kg mass is 5 m from the end of the surface;
a) maximum speed does it reach before crashing to into the pulley?
b) How much time does it take for it to crash into the pulley?

Edit: Finished it. I had the wrong time and showed up early for my exam. Here you go:

[Infinity.]

Could you tell me What's this P Versus NP problem all about? A famous Math Problem.

[Feynman]

Could you tell me What's this P Versus NP problem all about? A famous Math Problem.

That's computer science, actually. It's not my specialty.

[Infinity.]

All right so 1 for Probability.

Its a 4 Digit number 0000-9999

And a Lucky number is consider when Sum of first 2 digits equals Sum of last 2 digits

Like 2222 , 2+2=2+2

Likewise If a 4 digit number is Picked at random then Whats the probability that its a Lucky Number?

[Feynman]

All right so 1 for Probability.

Its a 4 Digit number 0000-9999

And a Lucky number is consider when Sum of first 2 digits equals Sum of last 2 digits

Like 2222 , 2+2=2+2

Likewise If a 4 digit number is Picked at random then Whats the probability that its a Lucky Number?

I don't do stats/probability. I should have added that to the list.

[Infinity.]

Somewhere Further down the question there is Binomial Theorem Used, Which is an Algebra Topic.

[Feynman]

Somewhere Further down the question there is Binomial Theorem Used, Which is an Algebra Topic.

But still revolves around probability. I've used binomial theorem, but only sparsely, and not enough to help with a problem.

[Infinity.]

Yeah its lot more complicated and Confusing , anyways Thanks for your time and help.

We'll post here with Further Doubts.

[Feynman]

Somewhere Further down the question there is Binomial Theorem Used, Which is an Algebra Topic.

I kind of knocked the question away before even looking at it, because I saw it was probability-related. My apologies:

Let x represent the first two digits, and y represent the last two.

x + y = 0 -> 1 case (0000)
x + y = 1 -> 4 cases (1010,1001,0101,0110)
x + y = 2 -> 9 cases (1111,1120,1102,2011,2020,2002,0211,0220,0202)
x + y = 3 -> 16 cases
.
.
.
There appears to be a pattern. Skip to the end and work backwards to see if it continues.
.
.
.
x + y = 18 -> 1 case (9999)
x + y = 17 -> 4 cases (9898,8989,9889,8998)
x + y = 16 -> 9 cases

So we have the same pattern starting from x+y=0 and moving forward, and starting from x+y=18 and moving backwards. The only number of cases that doesn't repeat is 100 cases, when x+y=10.

If 100 cases repeated, we'd have:

Total cases = Summation of i² from i=1 to i=10 = 770

However, 100 cases only appears once, so we have:

Total cases = (Summation of i² from i=1 to i=10) - 100 = 670

So there are 670 magic numbers between 0000 and 9999.

I think that's right, but I don't know how to do the probability part.

[Infinity.]

Actually the probability is coming to 670/10000, And you seem to have cracked it,
Thanks a lot, and also The solution in which Binomial was used was Way too complicated, But your method was bit too easy and understandable.

[Feynman]

Actually the probability is coming to 670/10000, And you seem to have cracked it,
Thanks a lot, and also The solution in which Binomial was used was Way too complicated, But your method was bit too easy and understandable.

Do you have the other solution? I'd like to see it.