Physics: Post your doubts here!

[Heba Nazir]

HELPPP.
The pressure at sea level is 100000Pa. The density of sea water is 1030kg/m3. What is the approximate pressure 80m below the surface of sea? Answer is 900000Pa. How

first,you might want to separate the data.
density=1030
h=80
g=9.81
P=dgh=1030*9.81*80=808344
we get the answer 900000 by adding 100000Pa to 808344 which is 908344 which is approximately 900000.this is because the pressure applied 80m below the sea level is not just the waters pressure,but also the atmospheric pressure.
i hope this helps,even though my explanation seems all over the place.

 

[Heba Nazir]

I NEED HELP WITH THEORY(P22).
i always blank out and seem to remember nothing when im attempting the past papers.i just cant solve them.
i need some guidance regarding how i should solve the theory paper and i need it really quick as i will be attempting the october/november retakes

 

[Najahh]

I NEED HELP WITH THEORY(P22).
i always blank out and seem to remember nothing when im attempting the past papers.i just cant solve them.
i need some guidance regarding how i should solve the theory paper and i need it really quick as i will be attempting the october/november retakes

SAME PROBLEM!!

 

[Daniel Jeng]

HELP!
June 2004 Paper 4 Question 3
I'm stuck in doing 3 (b).View attachment 62682
The mark scheme says both stars have the same centripetal force, but how do I know that?

The 2 stars have the same centripetal force as the gravitational force provides the centripetal force. This means the gravitational force acting on each object has the same magnitude, using the equation GMm/r^2.

 

[fatimaw]

Hi everyone, AsSalamoAlaikum Wr Wb...

I just started chem AS CAN ANYONE HELP ME !!! I dont get this percentage error like why is it -0.01 and not 0.005 (question B) i thought we always divide it???

 

[Daniel Jeng]

I just started chem AS CAN ANYONE HELP ME !!! I dont get this percentage error like why is it -0.01 and not 0.005 (question B) i thought we always divide it???View attachment 62715

This is the physics thread, not the chemistry thread. Go ask there, not here.

 

[Unknown202]

The helium in the cylinder has a volume of 6.0 × 10–3 m3 (0.0060 m3) and is at a pressure of
2.75 × 106 Pa.
(i) The pressure of helium in each balloon is 1.1 × 105 Pa. The volume of helium in an inflated
balloon is 3.0 × 10–3 (0.0030 m3). The temperature of the helium does not change.

Calculate the number of balloons that were inflated.
octnov2014 p31 Q7(b) I knew the pv=p2v2 method bit how could ik that v2 is the cylinder and balloon volume which is 0.15 as pressure p2 was only pressure inside balloon help cuz iam confused

 

[Daniel Jeng]

The helium in the cylinder has a volume of 6.0 × 10–3 m3 (0.0060 m3) and is at a pressure of
2.75 × 106 Pa.
(i) The pressure of helium in each balloon is 1.1 × 105 Pa. The volume of helium in an inflated
balloon is 3.0 × 10–3 (0.0030 m3). The temperature of the helium does not change.

Calculate the number of balloons that were inflated.
octnov2014 p31 Q7(b) I knew the pv=p2v2 method bit how could ik that v2 is the cylinder and balloon volume which is 0.15 as pressure p2 was only pressure inside balloon help cuz iam confused

I am fairly certain that the easiest way of calculating this is to find out how many moles of helium gas are in the cylinder and each balloon, then finding how many balloons can be filled. You should use the equation PV=nRT to do this. Use the equation to find out the number of moles of helium in the cylinder and in one balloon, then divide the number of moles of the gas in the cylinder by the number in one balloon to find out how many balloons can be filled. Because the temperature of the gas doesn't change, you can literally use any temperature as a placeholder in the equation. Just make sure you use the same temperature in all calculations you do.

 

[dumbledore.]

Ans = D
How??

 

[Daniel Jeng]

Ans = D
How??

Say that one arrow is equal to 1F (arbitrary value).
A gives no resultant torque, but a resultant force of 1F upwards. B gives both a resultant torque and a resultant force of 1F upwards. C gives no resultant torque or force. D gives zero resultant force but a resultant torque. If you extend the force lines, any line that crosses the centre of the circle will not provide a torque. However any force lines will always exert a force on the circle, even if it provides a torque at the same time.

 

[dumbledore.]

Say that one arrow is equal to 1F (arbitrary value).
A gives no resultant torque, but a resultant force of 1F upwards. B gives both a resultant torque and a resultant force of 1F upwards. C gives no resultant torque or force. D gives zero resultant force but a resultant torque. If you extend the force lines, any line that crosses the centre of the circle will not provide a torque. However any force lines will always exert a force on the circle, even if it provides a torque at the same time.

Thankyou

 

[Astralgod]

Guys i did my mock AS practical paper today and it was a simple pendulum with different masses attached. we were to measure the period T. so this question states to make a table with six sets of readings and draw a graph( i think you'll know this process). but anyways i measured T wrong instead of 1 complete swing from point A to Point A i counted period From Point A to Point B. will i lose all my 20 marks or will i get Error carried forward and only lose 2-3 marks.... pls. clarify this. i need to re access my future then.

 

[Daniel Jeng]

Guys i did my mock AS practical paper today and it was a simple pendulum with different masses attached. we were to measure the period T. so this question states to make a table with six sets of readings and draw a graph( i think you'll know this process). but anyways i measured T wrong instead of 1 complete swing from point A to Point A i counted period From Point A to Point B. will i lose all my 20 marks or will i get Error carried forward and only lose 2-3 marks.... pls. clarify this. i need to re access my future then.

No, I don't think the examiners would be so harsh as to subtracting all 20 marks in the section, however I don't think you will only lose 2-3 marks either. Sometimes the marking schemes doesn't state what range of values you should get for the answer in one particular question, but sometimes they do. There you would be losing 1 or 2 marks extra. My estimate is that you would lose about 5 marks or so, but definitely not the whole 20 marks just by using the wrong period.

 

[Astralgod]

No, I don't think the examiners would be so harsh as to subtracting all 20 marks in the section, however I don't think you will only lose 2-3 marks either. Sometimes the marking schemes doesn't state what range of values you should get for the answer in one particular question, but sometimes they do. There you would be losing 1 or 2 marks extra. My estimate is that you would lose about 5 marks or so, but definitely not the whole 20 marks just by using the wrong period.

Daniel you made my day...
Thank you man. Because i know ill get at least 30+ marks for practicals now, i was worried i would lose all my marks, 5 marks is good either way. Thanks again, for clearing that up.

 

[Daniel Jeng]

Daniel you made my day...
Thank you man. Because i know ill get at least 30+ marks for practicals now, i was worried i would lose all my marks, 5 marks is good either way. Thanks again, for clearing that up.

Well, you're welcome However it's still not 100 percent that you will get 30+ as there might be some oversight you made that you didn't realise. Also, those 8 marks at the end of each of those paper... they're the hardest imo last year. You think you did alright in those?

 

[Astralgod]

Well, you're welcome However it's still not 100 percent that you will get 30+ as there might be some oversight you made that you didn't realise. Also, those 8 marks at the end of each of those paper... they're the hardest imo last year. You think you did alright in those?

It was a lens prac. with the usual limitations/improvements, which came in 2015/M/J/34 so i memorized those 8 points since it was more or less the same prac. Also, out of 8 marks 2 is always inbuilt which is 2 readings not enough and get more readings and plot a graph. That's why i was confident. Before the exam i posted a thread on forum asking what might come for the exam, lo and behold someone said lens practicals and electricity. so she was half right as the other prac was pendulum and mass alterations and i was glad cuz(electricity pracs is my weakest suit). But in the heat of the moment i counted periods wrong for the pendulum.. But since you pointed out that examiners wouldn't be too harsh i felt better. Even 8 marks cut off would be allright at this point since i checked with my tutor what i wrote for the exam.

 

[Daniel Jeng]

It was a lens prac. with the usual limitations/improvements, which came in 2015/M/J/34 so i memorized those 8 points since it was more or less the same prac. Also, out of 8 marks 2 is always inbuilt which is 2 readings not enough and get more readings and plot a graph. That's why i was confident. Before the exam i posted a thread on forum asking what might come for the exam, lo and behold someone said lens practicals and electricity. so she was half right as the other prac was pendulum and mass alterations and i was glad cuz(electricity pracs is my weakest suit). But in the heat of the moment i counted periods wrong for the pendulum.. But since you pointed out that examiners wouldn't be too harsh i felt better. Even 8 marks cut off would be allright at this point since i checked with my tutor what i wrote for the exam.

As long as it's all sorted out, that's pretty good to hear

 

[Astralgod]

It's sorted, but i'm still pondering the graph question as in the pendulum thing. Do you really think that they won't be harsh?

 

[Daniel Jeng]

It's sorted, but i'm still pondering the graph question as in the pendulum thing. Do you really think that they won't be harsh?

Graphs huh... I'm not exactly sure in paper 3s, but in paper 5s they normally have an exemplar they place over to see if it lines up. In the case of paper 3s it might be the same, so I would expect a few marks to be taken there as well. But that would be something like 1 or 2 marks only I suspect. Like I said they do give ecfs and the graph will be getting marks. If you're unsure just check the marking schemes of the graphs again, and see where you might lose marks. The way they mark those are basically the same anyways.

 

[Astralgod]

Graphs huh... I'm not exactly sure in paper 3s, but in paper 5s they normally have an exemplar they place over to see if it lines up. In the case of paper 3s it might be the same, so I would expect a few marks to be taken there as well. But that would be something like 1 or 2 marks only I suspect. Like I said they do give ecfs and the graph will be getting marks. If you're unsure just check the marking schemes of the graphs again, and see where you might lose marks. The way they mark those are basically the same anyways.

yeah i asked cuz the readings of wrong time periods were entered to plot the graph thats why.