Physics: Post your doubts here!

[Thought blocker]

ans is B, can anyone help me do it?

Here https://in.answers.yahoo.com/question/index?qid=20170805181222AAMboi8

 

[dumbledore.]

A certain organ pipe, closed at one end, can resonate at consecutive frequencies of 640 Hz, 896 Hz, and 1152 Hz. Deduce its fundamental frequency.

 

[dumbledore.]

A pile driver supported by a crane is used to drive a vertical steel girder of mass 900kg into the ground. The pile driver has an 80g steel 'hammer' which is raised 4.0m above the top end of the girder then released to strike the end of the girder and drive it further into the ground. Each impact drives the end of the girder 0.4m further into the ground. Assuming the pile driver does not bounce, calculate:

1. the speed of the pile driver just before impact? ans: 8.94m/s
2. the speed just after impact? ans: 0.730m/s
3. the force of friction on the girder as it penetrates the ground? ans:653N

 

[amina1300]

I have the components B B D and an overall C should I give a retake?

In my AS..

 

[Metallic9896]

I have the components B B D and an overall C should I give a retake?

In my AS..

If I were you I would hands down give a retake, given that I'd be aiming for an A*. Even turning this C into a B would be a tougher job. So definitely go for a retake and don't sweat it, you'll do great. I firmly believe any person who has the awareness and dedication to take out time and come to this forum is deserving of an A*. Good luck! We're all here to help, feel free to ask any and all queries about any and all matters, whether they are past paper questions or about effective studying techniques.

 

[Unknown202]

A person uses a surfboard to ride every 30th wave crest towards the beach. The wave crest
travels at a speed of 1.6m/ s and the distance between each wave crest is 24m.
How many wave crests does the person surf in one hour? plzzzzzzzz i need a help in tht question

 

[Metallic9896]

A person uses a surfboard to ride every 30th wave crest towards the beach. The wave crest
travels at a speed of 1.6m/ s and the distance between each wave crest is 24m.
How many wave crests does the person surf in one hour? plzzzzzzzz i need a help in tht question

Is the answer 8?

 

[studyingrobot457]

A person uses a surfboard to ride every 30th wave crest towards the beach. The wave crest
travels at a speed of 1.6m/ s and the distance between each wave crest is 24m.
How many wave crests does the person surf in one hour? plzzzzzzzz i need a help in tht question

Very easy, In fact, it can be solved using IGCSE knowledge

first of all the wavelength(lambda) =24 m
velocity= 1.6 m/s
so frequency = v/(lambda) = 1.6/24 (not going to reduce to decimal, you will know later)

and since frequency = 1/time period so time period = 1/freq =1/1.6/24= 24/1.6 = 15 s

so if every wave takes 15 s and he rides the 30th only this means he will wait 15*30 = 450 s for each 30th wave

his means total of 3600/450 = 8 waves he surf in an hour
hope that helps

 

[anastasia grey113]

http://papers.gceguide.com/A Levels/Physics (9702)/9702_s11_qp_42.pdf
http://papers.gceguide.com/A Levels/Physics (9702)/9702_s11_ms_42.pdf
Q3 part a
i even checked the mark scheme but i still dont seem to get it :/

 

[studyingrobot457]

http://papers.gceguide.com/A Levels/Physics (9702)/9702_s11_qp_42.pdf
http://papers.gceguide.com/A Levels/Physics (9702)/9702_s11_ms_42.pdf
Q3 part a
i even checked the mark scheme but i still dont seem to get it :/

I am an IGCSE student, but this seems very easy, if it is to store charge, this means that there should be charge difference in the scalar quantity of both, the very fact that charge moves away when more charge is added means it doesn't store charge, but it does store potential energy of the charge present, meaning that charge is same, in both cases, but it takes energy to get them in a separate way, and it releases energy when they are in the ground state

hope this explanation helps

 

[studyingrobot457]

http://papers.gceguide.com/A Levels/Physics (9702)/9702_s11_qp_42.pdf
http://papers.gceguide.com/A Levels/Physics (9702)/9702_s11_ms_42.pdf
Q3 part a
i even checked the mark scheme but i still dont seem to get it :/

more explanations:

https://www.quora.com/Does-capacitor-store-charge-or-energy-or-both


you also need to think of a capacitor as a complete system, not only on one side

 

[krishnapatelzz]

 

[Metallic9896]

http://papers.gceguide.com/A Levels/Physics (9702)/9702_s11_qp_42.pdf
http://papers.gceguide.com/A Levels/Physics (9702)/9702_s11_ms_42.pdf
Q3 part a
i even checked the mark scheme but i still dont seem to get it :/

Ahh yeah this is a classic question. Basically something CIE expects you to know and likes to check from time to time.

What does a capacitor do? What actually happens when a capacitor is placed in a circuit? Electrons begin flowing from one end of the circuit, right? Then they hit the first plate and stop. So we have a negative charge on one plate. But what happens next? Electrons from the adjacent plate are drawn away and fed back to the battery, leaving behind a lack of electrons on the second plate, also known as a positive charge. So tell me. Did you store any charge on the capacitor? In all honesty, you didn't. One plate is negative, the other is positive. What does that mena? It means an overall ZERO charge. On the other hand, those electrons reallllyyyy want to cross over through the gap or insulation between the plates and get to the other end, but the capacitor does not allow that, and thus, effectively, maintains a potential difference between the two ends. THIS is how it stores energy. Energy is the capacity to do work. And the capacitor (no pun intended) certainly has that capacity for you can use it to drive a circuit when it discharges. Basically, another way to look at it is that as the electrons accumulate on the negative plate, for the first time, they didn't face any resistance. However, once a good amount of electrons did get there, the next bunch of electrons would feel repulsion, however, the capacitor does work to bring them there and keep the charges separated on the plates. In this way, as it has done work, the energy is stored in it. https://www.quora.com/How-does-a-capacitor-store-energy Try reading this, I hope it helps.

 

[teachyourself]

something for physic's students to enjoy

 

[studyingrobot457]

something for physic's students to enjoy

I sometimes wonder, do really people don't know the basics (special relativity, general relativity , quantum mechanics and superposition, string theory, etc)

 

[teachyourself]

I sometimes wonder, do really people don't know the basics (special relativity, general relativity , quantum mechanics and superposition, string theory, etc)

yes and these are not 'basics' when you really delve into the detail and work with these theories, for many students even after clearing their A-levels thought experiments are a big problem, due to the excessive focus on academic questions
reading about a theory in the O' levels, A' levels, popular science books and Wikipedia is one thing and then studying it in an undergrad and graduate program is another, then also comes in the difference of using observations to understand the results and connecting them to the theory versus just thinking about a theory and doing the math, this being the difference between theoretical physicists and experimental astrophysicists
https://physics.stanford.edu/research/experimental-observational-astrophysics-and-cosmology
https://physics.stanford.edu/research/theoretical-astrophysics-and-cosmology
https://www.quora.com/What-is-the-d...cist-astrophysicist-and-theoretical-physicist
if it was so easy and basic then quantum mechanics and general relativity would have been reconciled long time ago, it is precisely because it is NOT easy that astrophysicists have not been able to understand quantum mechanics completely and the information paradox remains an unsolved issue
there is one attempt in this paper
https://arxiv.org/pdf/1601.00921v1.pdf

 

[studyingrobot457]

yes and these are not 'basics' when you really delve into the detail and work with these theories, for many students even after clearing their A-levels thought experiments are a big problem, due to the excessive focus on academic questions
reading about a theory in the O' levels, A' levels, popular science books and Wikipedia is one thing and then studying it in an undergrad and graduate program is another, then also comes in the difference of using observations to understand the results and connecting them to the theory versus just thinking about a theory and doing the math, this being the difference between theoretical physicists and experimental astrophysicists
https://physics.stanford.edu/research/experimental-observational-astrophysics-and-cosmology
https://physics.stanford.edu/research/theoretical-astrophysics-and-cosmology
https://www.quora.com/What-is-the-d...cist-astrophysicist-and-theoretical-physicist
if it was so easy and basic then quantum mechanics and general relativity would have been reconciled long time ago, it is precisely because it is NOT easy that astrophysicists have not been able to understand quantum mechanics completely and the information paradox remains an unsolved issue
there is one attempt in this paper
https://arxiv.org/pdf/1601.00921v1.pdf

You think we are given these at high school education, you have to be mistaken, I mean if you don't know about time dilation, Schrödinger equation, and Heisenberg uncertainty principle, then what you know about physics, kinematics?

 

[studyingrobot457]

and when did I talk about experimental astrophysics, please keep things correlated

 

[teachyourself]

firstly i am glad that at-least someone your age is interested in science for the sake of understanding it rather than just grades or the awful rote memorisation, hopefully you will become a great scientist one day

You think we are given these at high school education, you have to be mistaken

precisely my point this is not a part of high school education, even if it were, it would be superficial at best, so if people do not know about this stuff it is completely okay for them not to know about

I mean if you don't know about time dilation, Schrödinger equation, and Heisenberg uncertainty principle, then what you know about physics, kinematics?

1.knowing, 2.understanding and 3.applying are three very different things, you will understand that when you will reach the graduate level of any of the natural or pure sciences

so for your question

...then what you know about physics, kinematics?

the answer is that students know only a few formulas and a few ideas and facts that they have to memorize, the very reason why students end up hating science

science and history as subjects are not about rote memorisation facts but about questioning and understanding the natural phenomenon as far as science goes; and for history it is to understand how our ideas have changed and we can improve/change as far as public policy, intellectual development and our values go

while you might have an interest in trying to understand the more complex theories of science, many other students very much like you are discouraged to do so specially by teachers and parents with the claim "focus on your studies" which is actually harmful, which is why musing over the idea "I sometimes wonder, do really people don't know the basics" does not help, if you know more help others get to know more

the appropriate way to study the sciences is to break down the biggest questions into the basic concepts (which is i think what you are doing), so that you can go backwards from the complex theories to the most basic ones, which can also be chronological to some extent, more importantly it shows the purpose of science that being finding out about

 

[teachyourself]

and when did I talk about experimental astrophysics, please keep things correlated

actually it is correlated because one area of this field deals with the concepts and mathematical models and the other uses observations and experiments to test those mathematical models and theories, without understanding the effort required to develop the theories you mention as "basic" you will not be prepared for the hard work required at the undergrad and graduate level, the theories you mentioned are NOT basic by any means you will only understand that when you enter the field or are at graduate level, most students simply cannot cope with the mathematics required and drop out

so to demonstrate the amount of time/effort required
one example for Einstein to find e=mc2 and then test it
http://www.stresscure.com/hrn/einstein.html (there are better links)
another example Einstein theorized Gravitational Waves (not Gravity Waves) and after 40 years of consistent work the Gravitational Waves were detected using the LIGO
https://www.ligo.caltech.edu/news/ligo20160211
https://www.theguardian.com/science...on-gives-hints-on-dark-matter-and-black-holes

so when you look at the theories you mentioned in an in-depth then the mathematics and the observation required to confirm the mathematics becomes VERY challenging, so calling these theories as "basic" is incorrect these are advanced theories that is why even at the A-levels the syllabus requires you to just skim through it at best, to understand the true complexity of these theories you need to understand the math required
https://www.quora.com/What-kinds-of-math-do-you-use-majoring-in-astrophysics
if you still find these theories as basic and can do the mathematics in your mind the way Stephen Hawking does it, then you should attempt working on a side project and hand it over to universities when applying

one more thing to note is that some graduate student programs (in top unis graduate means Phd because of the assumptions that an MSc student in the natural and pure sciences will try for a Phd) require a foreign language
http://math.mit.edu/academics/grad/timeline/language.php