a little help in physics??

[Just call me MJ]

Hi! I am doing AS and I am having a hard time doing paper 1 although I just finished studying the syllabus!! Its 1 of two things:
1 : either I am doing the ones for A2
2 : I need to study physics all over again!!!!​

Can you please give me some tips for paper 1?!?!?!?​

I also have a question:
paper 1, may/june 2009, Q15, why is the answer mgh/4 ????? isn't it supposed to be 0!?!? cause water lost gpe in the first container and gained it back in the second empty container!!!!!???? right?PLEASE HELP!!!​

And thank you in advance!!!​

 

[Doctor Nemo]

Hi! I am doing AS and I am having a hard time doing paper 1 although I just finished studying the syllabus!! Its 1 of two things:​

1 : either I am doing the ones for A2​

2 : I need to study physics all over again!!!!​

Can you please give me some tips for paper 1?!?!?!?​

I also have a question:​

paper 1, may/june 2009, Q15, why is the answer mgh/4 ????? isn't it supposed to be 0!?!? cause water lost gpe in the first container and gained it back in the second empty container!!!!!???? right?PLEASE HELP!!!​

And thank you in advance!!!​

It can not be zero because some of the water is at a lower level than at the start. How to calculate the loss?

At first it seems very difficult because each layer of water initially has a different amount of potential energy. Then one remembers that the problem can be simplified by the use of the centre of gravity. The top half of the water on the left has fallen. The centre of gravity of this half is located 1/4 above the bottom half. When the levels are the same in the two vessels the centres will be 1/4h so the centre of the top half of water fell h/2. So the loss is mgh, 1/2 the mass fell a distance of 1/2h and the result is 1/4mgh.

Alternatively one can think of the total mass together having a centre of gravity of h/2 before and h/4 after. This is equivalent to the entire mass falling h/4 so the loss is again mgh/4.

I think this is a pretty hard question. According to the exam report only 15% got it right.

 

[Xenon]

Hi! I am doing AS and I am having a hard time doing paper 1 although I just finished studying the syllabus!! Its 1 of two things:​

1 : either I am doing the ones for A2​

2 : I need to study physics all over again!!!!​

Can you please give me some tips for paper 1?!?!?!?​

1. If you go through recent papers (2002 onwards), you won't find any questions from A2 syllabus. You might find them if you go through topical redspots but still you'll be able to filter those out
2. It won't hurt you if you go through the whole syllabus again but when you revise the syllabus again, do question papers along with it... it'll be a more productive approach
now, first of all, don't get frustrated because you are making mistakes... do all the recent papers once at first and then do all of them again... try to understand what mistakes you make every time and rectify them...
actually I'm not surprised that you are having a hard time since you just finished the syllabus, it happens that while you have completed and even understood what the book says, you might be failing to understand it's application... this is where solving past papers come into aid... now the more you practice, the better you'll get... lemme tell you about myself, I used to take more than 1 hr initially with considerable mistakes... but after practicing, it occurred that I would finish a paper with times to spare and also scored high marks, sometimes full... the whole thing is a gradual process... just keep on practicing

 

[Just call me MJ]

Thanks alot you guys! this has pulled me out of the grave! I almost gave up to the fact that I suck at physics! But now I guess I'll do exactly what you said!!! And hope for better results!!!!!!
thanks a million!

 

[Just call me MJ]

question 6 may/june 2011 paper 11?!?!?!?!?!?!?!?!?!?!?

 

[Doctor Nemo]

question 6 may/june 2011 paper 11?!?!?!?!?!?!?!?!?!?!?

Ok, I was fooled by this one too. You have to remember that the total velocity is the area under the graph since a =dv/dt so dv = a dt then if you integrate both sides you get the velocity. If you imagine adding up the area under the acceleration graph it first increases at in increasing rate, then at at the top of the graph it is increasing at a constant rate and then the rate of increase slows down until the INCREASE in velocity is zero and so the velocity will be constant. Since the acceleration is always positive the velocity is always increasing. So the answer is A. I mixed up the relationship between the acceleration and velocity and was thinking too carelessly that the velocity was the derivative of acceleration. So I imagined how the tangent to the acceleration curve would behave and picked C.

If the graph had been velocity then the answer would have been C for acceleration.

Doing MCQ is very much like walking through a field where there have been a lot of cows grazing. You have to always be very careful where you step.

 

[Just call me MJ]

@Doctor Nemo!! If you have a question to ask, then who on god's green earth can help you!?!? I mean you simply know all the answers! and they all make sense!!! Surprisingly! cause I am a total dumb ass when it comes to physics and now I feel like I know everything thanks to you!
What is your real age?!?!?
And how did you study these exams!?!? and still know everything!?!?
Please tell me your study plan!! and are you this great with any other subjects!??!??!

and 1 more question! paper 12 may/june 2011 Q6 and 16?????
and Q 35, paper 1, may/june 2002!

 

[Just call me MJ]

And sorry for bugging you like that! but quite frankly you are the only one that could help me through!! and I am scared to death from this particular subject!!! I don't know why!! but I just get a HUGE HEADACHE when I do this!!( PHYSICS)
Although the subject is quite brilliant and I love it! but there's just too much! I'd rather study biology and chemistry than physics! although I love physics more than the rest of them!!
What should I do?!? I mean I study and study but I get the same results over and over again!

Please help me! I'm knocking on collage door! and physics is HUGE for the major I am going through!

Sorry for rambling on and on but I really need you help!

Thank you for your time in advance!

 

[Doctor Nemo]

And sorry for bugging you like that! but quite frankly you are the only one that could help me through!! and I am scared to death from this particular subject!!! I don't know why!! but I just get a HUGE HEADACHE when I do this!!( PHYSICS)
Although the subject is quite brilliant and I love it! but there's just too much! I'd rather study biology and chemistry than physics! although I love physics more than the rest of them!!
What should I do?!? I mean I study and study but I get the same results over and over again!

Please help me! I'm knocking on collage door! and physics is HUGE for the major I am going through!

Sorry for rambling on and on but I really need you help!

Thank you for your time in advance!

Well, if you love physics then you should be able to make friends with it (him? she?) and have a very constructive relationship. You should enjoy the subject.

First do not allow yourself to fall into a state of panic. The only time in life you are allowed to do that is when you are in a plane and the wings fall off.

The program of review in preparation for the exams that I recommend is briefly as follows. It is based on the fact that what you need to know for the exams is a combination of what is in the syllabus and what has been on the past papers.

Go through the content of the syllabus. Try to subdivide each topic in terms of the types of questions on the exams. As you read each line ask yourself if you understand that material and the kinds of questions that can be asked about that it.

Once you feel you know the material of a topic only then go to the past papers and practice ONLY the questions on that topic. I do not think it is a good idea to practice entire papers but focus only on one topic at a time and do all the questions on that one topic. In this way you will become familiar with all the types of questions that can be asked about that topic and will learn all that you are supposed to know about that topic.


When you have completed one topic then go on to the next and follow the same procedure, working your way through the syllabus. Stay with one topic until you have mastered it and you are confident that you can answer the questions. It is much better to know very well parts of the syllabus than to know only a little about all of it.

The idea is to build in you mind relationships between questions on the exam, the part of the syllabus upon which the question is based and what you are supposed to know about that part of the syllabus and the problem solving skills that you have developed for that part of the syllabus.

 

[Doctor Nemo]

@Doctor Nemo!! If you have a question to ask, then who on god's green earth can help you!?!? I mean you simply know all the answers! and they all make sense!!! Surprisingly! cause I am a total dumb ass when it comes to physics and now I feel like I know everything thanks to you!
What is your real age?!?!?
And how did you study these exams!?!? and still know everything!?!?
Please tell me your study plan!! and are you this great with any other subjects!??!??!

and 1 more question! paper 12 may/june 2011 Q6 and 16?????
and Q 35, paper 1, may/june 2002!

I have some difficulties pasting my comments on your questions.

Take the question from 12 may/june 2011 Q6. The first question your mind should ask is, “where is this question from in the syllabus?”

The exact place is “describe and explain motion due to a uniform velocity in one direction and a uniform acceleration in a perpendicular direction.”

The second question that your mind asks you is, “what am I supposed to know about this?” Your answer is that this is about falling objects with constant horizontal velocity. The two motions are independent of each other. A falling object with no horizontal velocity will hit the ground at the same time as an object with horizontal velocity. You can calculate how far an object will travel horizontally by calculating how long it takes for it to fall to the ground.

Third question your mind asks you is, “ok, how do I do these calculations?”

This takes to another part of the syllabus which you need to know very well.

“solve problems using equations that represent uniformly accelerated
motion in a straight line, including the motion of bodies falling in a
uniform gravitational field without air resistance”

The horizontal velocity is constant because there is no force and therefore no acceleration. The distance traveled is vt.

The distance the object falls is given by 1/2gt2 because the starting velocity in the vertical direction is zero.

Form the ratio like the question asks and then call up that part of your mind that does algebra.

vt
1/2gt2

Cancel terms, turn the 1/2 upside down to bring it up to the top with the result

2v
gt

This happily turns out to be one of the choices which is D and which is correct.

Q 16

Where in the syllabus? Moments of forces

define and apply the moment of a force and the torque of a couple

show an understanding that, when there is no resultant force and no resultant torque, a system is in equilibrium

apply the principle of moments.

What am I supposed to know?

Moment of a force = force X distance to where are calculating moments. If the object is in equilibrium then clockwise moments = counterclockwise moments. The point from which the moments can be calculated can be anywhere on the object and it is usually convenient to calculate them from where an unknown force is acting.

Pick a point from where to calculate the moments. The obvious choice is point X.

Identify the clockwise and counterclockwise moments and set them equal to each other; if necessary resolve forces into their x- and y-components.

Weight is clockwise, F is providing a counterclockwise moment about point X. However only the y-component is acting as a moment so need to calculate y-component. This is F x sin(30) (The X-component is acting to push the beam into the wall.)

The beam is uniform meaning that the centre of gravity is in the centre. Therefore the weight can be taken as acting 1/2 the length of the beam from X and force F is acting at a point a distance the length of the beam from X.

Form equation for moments.

10 x l/2 L = F x sin(30) L

where L is length of beam and which cancels giving F = 5/sin(30) = 10 N. So the answer is C.

Q 35, paper 1, may/june 2002

What makes this problem more difficult is that it requires knowledge of several different parts of the electricity syllabus-too many for me to list.

As current moves from the voltage source through the resistors it loses electrical potential energy.

The loss of voltage across R1 is 2 volts, that across R2 is 1 volt and that across R3 is 2 volts.

Alternatively you can think of the gain of potential energy as you move through the resistors from 0 potential.

As move up from 0 there is a gain across each resistor of electrical potential energy. Across R3 there is a gain of +2V, across R2 a gain of +1V and since the total gain must equal +5 volts the increase across R1 is also +2V.

Since the same current is passing through all the resistors the fact that the potential change across R1 and R3 is the same means that they must have the same resistance. Since the potential change across R2 is 1/2 that of R1 and R3 then it must have 1/2 of their resistance. So the answer is C.

 

[Just call me MJ]

Thank you very much! you really are a life savior!!
I am sorry for all your trouble and time, and I hope that this is the last time you hear from me!!! cause I'm such a headache! I know myself!
there is still one question which you didn't answer!
What is your real age?!?
Thank you again for your precious time and advise!