IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Sciences => Topic started by: nid404 on August 17, 2010, 09:07:58 am

Title: Physics help!
Post by: nid404 on August 17, 2010, 09:07:58 am: June 2010 paper 4 A2 physics.

Q1b. Can someone mark the position. Is it an estimate or what? :S

c. Why do we deduct the weight of the stone?
Title: Re: Physics help!
Post by: elemis on August 17, 2010, 09:12:05 am: https://studentforums.biz/pastpapers/mayjune-2010-papers-here!/15/ (https://studentforums.biz/pastpapers/mayjune-2010-papers-here!/15/)

Anyone wishing to help Ahana can view the past paper she is talking about by clicking the above link.

The MS is there too.

Good luck !
Title: Re: Physics help!
Post by: nid404 on August 17, 2010, 09:13:01 am: Thanks Ari :)
Title: Re: Physics help!
Post by: elemis on August 17, 2010, 09:15:03 am: Quote from: ~Ahana~ on August 17, 2010, 09:13:01 am
Thanks Ari :)

Mai hoo na ;)
Title: Re: Physics help!
Post by: nid404 on August 17, 2010, 11:23:32 am: Anyone? ::)
Title: Re: Physics help!
Post by: Saladin on August 17, 2010, 11:27:06 am: Have not gone that far :(

Wait for astar.
Title: Re: Physics help!
Post by: nid404 on August 17, 2010, 11:31:48 am: Not a problem :)

I don't have a choice :P
Title: Re: Physics help!
Post by: M-H on August 17, 2010, 01:05:16 pm: Quote from: ~Ahana~ on August 17, 2010, 09:07:58 am
June 2010 paper 4 A2 physics.

Q1b. Can someone mark the position. Is it an estimate or what? :S

c. Why do we deduct the weight of the stone?

i don't know anything about these cie papers..they're all in 30 :D..which's p4 ::)
i'll try to help
Title: Re: Physics help!
Post by: nid404 on August 17, 2010, 01:13:40 pm: Here. :)
Title: Re: Physics help!
Post by: nid404 on August 17, 2010, 03:26:46 pm: Yo :P
Title: Re: Physics help!
Post by: elemis on August 17, 2010, 03:35:21 pm: Quote from: ~Ahana~ on August 17, 2010, 03:26:46 pm
Yo :P

I really feel sorry for you...

Keep bumping this post - it may draw attention :)
Title: Re: Physics help!
Post by: nid404 on August 17, 2010, 03:37:26 pm: Quote from: Ari Ben Canaan on August 17, 2010, 03:35:21 pm
I really feel sorry for you...

Keep bumping this post - it may draw attention :)

-__-

Yeah help me so i don't have to post 10 times in a row...else it'll be called spamming :P
Title: Re: Physics help!
Post by: elemis on August 17, 2010, 03:40:04 pm: Quote from: ~Ahana~ on August 17, 2010, 03:37:26 pm
-__-

Yeah help me so i don't have to post 10 times in a row...else it'll be called spamming :P

Like this ? :P

SO what happened to Kratos ?
Title: Re: Physics help!
Post by: nid404 on August 17, 2010, 03:42:51 pm: Quote from: Ari Ben Canaan on August 17, 2010, 03:40:04 pm
Like this ? :P

SO what happened to Kratos ?

Yeah :D

He finds SF boring nowadays ::)
Title: Re: Physics help!
Post by: elemis on August 17, 2010, 03:49:28 pm: Quote from: ~Ahana~ on August 17, 2010, 03:42:51 pm
Yeah :D

He finds SF boring nowadays ::)

He's burnt out - LOL !! He was frigging crazy when he first joined. :D
Title: Re: Physics help!
Post by: nid404 on August 17, 2010, 03:51:08 pm: Quote from: Ari Ben Canaan on August 17, 2010, 03:49:28 pm
He's burnt out - LOL !! He was frigging crazy when he first joined. :D

He's still like that!!! Trust me. ::)
Title: Re: Physics help!
Post by: elemis on August 17, 2010, 03:52:30 pm: Quote from: ~Ahana~ on August 17, 2010, 03:51:08 pm
He's still like that!!! Trust me. ::)

I dont see him around much...

He's doing his A Levels ?
Title: Re: Physics help!
Post by: nid404 on August 17, 2010, 03:59:46 pm: Quote from: Ari Ben Canaan on August 17, 2010, 03:52:30 pm
I dont see him around much...

He's doing his A Levels ?

Yeah....busy studying I suppose. I talk to him on msn frequently though.
Title: Re: Physics help!
Post by: elemis on August 17, 2010, 04:05:36 pm: Quote from: ~Ahana~ on August 17, 2010, 03:59:46 pm
Yeah....busy studying I suppose. I talk to him on msn frequently though.

Yeah..... studying :P
Title: Re: Physics help!
Post by: M-H on August 17, 2010, 08:01:37 pm: Quote from: ~Ahana~ on August 17, 2010, 09:07:58 am
June 2010 paper 4 A2 physics.

Q1b. Can someone mark the position. Is it an estimate or what? :S

c. Why do we deduct the weight of the stone?
where's c in Q1 ???
guess you mixed up...?
Title: Re: Physics help!
Post by: nid404 on August 19, 2010, 07:03:51 am: Quote from: M-H on August 17, 2010, 08:01:37 pm
where's c in Q1 ???
guess you mixed up...?

b i) and ii)

BUMP!!!!! ::)
Title: Re: Physics help!
Post by: nid404 on August 20, 2010, 12:18:03 pm: Reminder M-H! :P
Title: Re: Physics help!
Post by: Saladin on August 20, 2010, 07:21:20 pm: The back-ground reading is the reading caused by cosmic rays and this not the object.

Therefore, the back-ground reading has to be 16 as the total sum of all the detector readings always ends up as 16. You need to remember here, that the object is not radiating anything. So, it is simply asking you about its absorption.

The second question is trying to ask you about the absorption ratio. In order to find that, you need to take away the cosmic radiation, and then find the ratio of the voxels.

So take away 16, and then do a ratio of all the present values.
Title: Re: Physics help!
Post by: nid404 on August 20, 2010, 07:24:28 pm: Oops. The question is on Circular motion :-X

lol that's fine...which paper do you see?
Title: Re: Physics help!
Post by: Saladin on August 20, 2010, 07:27:48 pm: Quote from: ~Ahana~ on August 20, 2010, 07:24:28 pm
Oops. The question is on Circular motion :-X

lol that's fine...which paper do you see?

The one that Ari uploaded.

Cna you upload the one you have a problem with!

No wonder, I was so jealous you got to got all the way to cosmology.

You can you give me the papers for the question you want?
Title: Re: Physics help!
Post by: nid404 on August 20, 2010, 07:33:01 pm: haha...

Q 1)b i) Only if you could mark the position.

I figured the second part.
Title: Re: Physics help!
Post by: Saladin on August 20, 2010, 07:36:07 pm: Quote from: ~Ahana~ on August 20, 2010, 07:33:01 pm
haha...

Q 1)b i) Only if you could mark the position.

I figured the second part.

I will do my best.
Title: Re: Physics help!
Post by: Saladin on August 20, 2010, 07:38:22 pm: Quote from: ~Ahana~ on August 20, 2010, 07:33:01 pm
haha...

Q 1)b i) Only if you could mark the position.

I figured the second part.

Alrite, I still have not done this yet. I hope to soon though.

Sorry. :-\
Title: Re: Physics help!
Post by: nid404 on August 20, 2010, 07:39:21 pm: Not a problem :)
Title: Re: Physics help!
Post by: nid404 on August 24, 2010, 09:01:38 am: Anyone ???
Title: Re: Physics help!
Post by: Vin on August 24, 2010, 09:02:23 am: Quote from: ~Ahana~ on August 24, 2010, 09:01:38 am
Anyone ???

Your Physics teacher. ::)
Title: Re: Physics help!
Post by: elemis on August 24, 2010, 09:17:16 am: Quote from: ~Vin~ on August 24, 2010, 09:02:23 am
Your Physics teacher. ::)

She's on holiday ::)
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 09:47:38 am: Can someone answer this please?

What is the meaning of viscous drag and upthrust?

For example: A submarine descends vertically at constant velocity. The three forces acting on the submarine
are viscous drag, upthrust and weight
Title: Re: Physics help!
Post by: nid404 on August 24, 2010, 09:55:38 am: Viscous drag- Resistance derived from friction between the surface of a body and the fluid through which it is moving. The fluid particles adjacent to the body slow down, causing turbulent flow. The magnitude of the drag depends on a number of factors; it increases with the relative velocity of fluid flow, the surface area over which the flow occurs; the roughness of the body surface; and the viscosity of the fluid.

Upthrust-Upthrust is the force that pushes an object up and makes it seem to lose weight in a fluid.
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 09:56:58 am: so then both are acting as resistive forces, right?
Title: Re: Physics help!
Post by: elemis on August 24, 2010, 09:58:35 am: Quote from: @d!_†oX!© on August 24, 2010, 09:56:58 am
so then both are acting as resistive forces, right?

From my limited knowledge of A Level Physics :

Upthrust is acting against the weight of an object in water hence I would suspect it is resistive.

I might be wrong. :-\
Title: Re: Physics help!
Post by: nid404 on August 24, 2010, 10:00:24 am: Quote from: @d!_†oX!© on August 24, 2010, 09:56:58 am
so then both are acting as resistive forces, right?

Both are resistive forces but their action is in different directions.
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 10:02:46 am: Alright, I think I should post the complete question itself:

A submarine descends vertically at constant velocity. The three forces acting on the submarine
are viscous drag, upthrust and weight.

Which relationship between their magnitudes is correct?

A weight < drag
B weight = drag
C weight < upthrust
D weight > upthrust
Title: Re: Physics help!
Post by: Vin on August 24, 2010, 10:06:21 am: I suppose it's D. But the velocity is constant. In the case of D, I'm guessing the velocity would increase. :-\
Title: Re: Physics help!
Post by: elemis on August 24, 2010, 10:07:56 am: D ?

Because Drag (D) + Upthrust (U) = Weight (W)

Hence B is wrong.
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 10:11:01 am: If it was just weight and upthrust or weight and drag, thn according to simple IGCSE Physics, I would answer B, as at constant(terminal) velocity the downward forces must equal the upward forces. But the case is different here, with three forces acting. I neither know which year this question is from, nor do I have any mark scheme for this one.
Are you sure about this Ari?
Drag (D) + Upthrust (U) = Weight (W)
Title: Re: Physics help!
Post by: nid404 on August 24, 2010, 10:12:27 am: Quote from: @d!_†oX!© on August 24, 2010, 10:02:46 am
Alright, I think I should post the complete question itself:

A submarine descends vertically at constant velocity. The three forces acting on the submarine
are viscous drag, upthrust and weight.

Which relationship between their magnitudes is correct?

A weight < drag
B weight = drag
C weight < upthrust
D weight > upthrust

It's descending vertically, so viscous drag doesn't come into picture. A and B are out.
Now if the submarine is sinking, then Weight is greater than upthrust.
If upthrust is equal to the weight, the submarine will float on the surface
If upthrust is greater, submarine will thrown up the surface ::)
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 10:14:48 am: Quote from: ~Ahana~ on August 24, 2010, 09:55:38 am
Viscous drag- Resistance derived from friction between the surface of a body and the fluid through which it is moving. The fluid particles adjacent to the body slow down, causing turbulent flow. The magnitude of the drag depends on a number of factors; it increases with the relative velocity of fluid flow, the surface area over which the flow occurs; the roughness of the body surface; and the viscosity of the fluid.

Why do we exclude drag because of vertical motion? Is there something like that in the definition? ::)
Title: Re: Physics help!
Post by: elemis on August 24, 2010, 10:18:21 am: It cant be B because there are 3 components involved.

B suggests that only two are present and hence equivalent..... the third force all must have some value thus B cant be correct.
Title: Re: Physics help!
Post by: nid404 on August 24, 2010, 10:20:39 am: Quote from: @d!_†oX!© on August 24, 2010, 10:14:48 am
Why do we exclude drag because of vertical motion? Is there something like that in the definition? ::)

Wait. Have a look at this.

(http://www.hydramotion.com/images/Viscous_drag.gif)

Like I said, drag and upthrust both act as resistive forces but their direction of action are different. Upthrust is the push on the object(acts vertically) and viscous drag opposes motion through the fluid (horizontal)
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 10:23:47 am: Ohh!! Thanks a lot Nid! The diagram made it so much easier :)

But hey wait, so what is the answer? :P
Title: Re: Physics help!
Post by: Vin on August 24, 2010, 10:24:51 am: Quote from: @d!_†oX!© on August 24, 2010, 10:23:47 am
Ohh!! Thanks a lot Nid! The diagram made it so much easier :)

But hey wait, so what is the answer? :P

yeah it did. :)

LOL!!
Title: Re: Physics help!
Post by: nid404 on August 24, 2010, 10:28:51 am: Quote from: @d!_†oX!© on August 24, 2010, 10:23:47 am
Ohh!! Thanks a lot Nid! The diagram made it so much easier :)

But hey wait, so what is the answer? :P

LOL! A and B are out cause drag's not in the picture.

C is not possible ::) If upthrust is greater, submarine is flung out of the water ::)

So it's D.
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 10:30:53 am: Thanks once again Captain Nid ! ;)
Title: Re: Physics help!
Post by: nid404 on August 24, 2010, 10:31:48 am: Quote from: @d!_†oX!© on August 24, 2010, 10:30:53 am
Thanks once again Captain Nid ! ;)

At your service :D
Title: Re: Physics help!
Post by: elemis on August 24, 2010, 02:19:16 pm: Cool, I was right :P
Title: Re: Physics help!
Post by: MasterMath on August 24, 2010, 03:56:05 pm: I actually think there is a drag force .. but yeah D is the most reasonable one :P
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 05:23:45 pm: can someone help me in this question?
Title: Re: Physics help!
Post by: Vin on August 24, 2010, 05:30:55 pm: Quote from: @d!_†oX!© on August 24, 2010, 05:23:45 pm
can someone help me in this question?

I'm guessing it's C. :-\
Title: Re: Physics help!
Post by: Saladin on August 24, 2010, 05:33:31 pm: Quote from: @d!_†oX!© on August 24, 2010, 05:23:45 pm
can someone help me in this question?

The answer is C.

The moments about a point is the force times he perpendicular distance.

Use trigonometry to find the length d.

Then you simply times this by 2N, to get the moments.

Then what you have to do is add the moments on the other side is also anti-clockwise.
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 05:39:28 pm: I am not sure either...there are so many things in my mind right now, each leading to different answer..

1) It can be A:
   Moment of a force = force X perpendicular distance
   Moment of a force = 2sin50 X 0.15 = 0.23 Nm
2) It can be C:
   Two forces acting simultaneously, thus two moments = 2 X 0.23 = 0.46 Nm
3) It can be D:
   My book (International A/AS level Physics - CIE endorsed) says -
The torque of a couple is the product of one of the forces and the perpendicular distance between the forces
Therefore, according to this, Torque = 2 X 0.15 = 0.60 Nm

Fortunately, I don't have any idea about B, or else I'd be dead =.=
Someone please help me!!
Title: Re: Physics help!
Post by: nid404 on August 24, 2010, 05:41:35 pm: Quote from: @d!_†oX!© on August 24, 2010, 05:23:45 pm
can someone help me in this question?

Force X perpendicular distance between the two forces

2sin50 X 0.3= 0.46Nm

C
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 05:43:06 pm: Oh I just realized, my 1) point is matching the 3) cause as the book says it is the perpendicular answer, so in that way 0.23 should be right.

Engraved, any say about my answers?
Ahana, the book says something else :/ it says only one of the forces..
Title: Re: Physics help!
Post by: Vin on August 24, 2010, 05:45:20 pm: Quote from: @d!_†oX!© on August 24, 2010, 05:43:06 pm
Oh I just realized, my 1) point is matching the 3) cause as the book says it is the perpendicular answer, so in that way 0.23 should be right.

Engraved, any say about my answers?
Ahana, the book says something else :/ it says only one of the forces..

I saw the book too. Pg. 107. But a different kind of an example is given. What does the markscheme say?
Title: Re: Physics help!
Post by: nid404 on August 24, 2010, 05:46:43 pm: Quote from: @d!_†oX!© on August 24, 2010, 05:43:06 pm
Oh I just realized, my 1) point is matching the 3) cause as the book says it is the perpendicular answer, so in that way 0.23 should be right.

Engraved, any say about my answers?
Ahana, the book says something else :/ it says only one of the forces..

In a couple the magnitude of the force is the same.
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 05:47:11 pm: Quote from: ~Vin~ on August 24, 2010, 05:45:20 pm
I saw the book too. Pg. 107. What does the markscheme say?

Right, page 107 it is. I don't have the mark scheme, nor do I know which year is this question from. I got this in the "topic-wise mcq"file i downloaded.
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 05:48:45 pm: Quote from: ~Ahana~ on August 24, 2010, 05:46:43 pm
In a couple the magnitude of the force is the same.

Oh I think I get it now..
Title: Re: Physics help!
Post by: Saladin on August 24, 2010, 05:49:38 pm: It has to be C, there is no other conclusion, the answer fits perfectly....
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 05:50:17 pm: Oh yes now know..sh*t!
what bloody say mistake I was doing...!!!

Thanks for your time Vin, Engraved and Captain Nid! :D
Title: Re: Physics help!
Post by: Vin on August 24, 2010, 05:51:29 pm: Quote from: @d!_†oX!© on August 24, 2010, 05:47:11 pm
Right, page 107 it is. I don't have the mark scheme, nor do I know which year is this question from. I got this in the "topic-wise mcq"file i downloaded.

Oh OK. Would you mind uploading the file here? :) Thanks. :)

Oh, no probs.
Title: Re: Physics help!
Post by: @d!_†oX!© on August 24, 2010, 05:54:40 pm: Oh sure, here it is. I got it from the link here:
https://studentforums.biz/reference-material-83/asa-level-physics-paper-1-topic-based/msg333437/#msg333437
Title: Re: Physics help!
Post by: Vin on August 24, 2010, 05:56:50 pm: Quote from: @d!_†oX!© on August 24, 2010, 05:54:40 pm
Oh sure, here it is. I got it from the link here:
https://studentforums.biz/reference-material-83/asa-level-physics-paper-1-topic-based/msg333437/#msg333437

Thank you for sharing! :) Though I've done very little out of the lot.
Title: Re: Physics help!
Post by: nid404 on August 25, 2010, 03:37:08 pm: Paper 4 Nov 08 Q3)b)ii)

Thanks :)
Title: Re: Physics help!
Post by: nid404 on August 26, 2010, 07:13:38 am: Anyone? :-\
Title: Re: Physics help!
Post by: Saladin on August 26, 2010, 12:15:13 pm: At time 0, there would be 0 displacement, so therefore, the needle would stay in it's original position meaning that it would stay as on the diagram. Basically meaning a maximum or minimum point because it goes from a max to a min. The machine does not start on the piece of cloth.

If displacement is 0, then it has to be in its original position.
Title: Re: Physics help!
Post by: nid404 on August 26, 2010, 01:59:38 pm: Quote from: Engraved on August 26, 2010, 12:15:13 pm
At time 0, there would be 0 displacement, so therefore, the needle would stay in it's original position meaning that it would stay as on the diagram. Basically meaning a maximum or minimum point because it goes from a max to a min. The machine does not start on the piece of cloth.

If displacement is 0, then it has to be in its original position.

Yup I got that. I asked for part b) The value of a is 11 :S Shouldn't it be 8(the original position)? :-\
Title: Re: Physics help!
Post by: cooldude on August 26, 2010, 02:05:15 pm: Quote from: ~Ahana~ on August 26, 2010, 01:59:38 pm
Yup I got that. I asked for part b) The value of a is 11 :S Shouldn't it be 8(the original position)? :-\

no, okay so first of all it is at its maximum position and it can travel a total of 22mm, that means the equilibrium position is 11mm below, now what is a, the amplitude (the maximum displacement from the mean position) so it is 11mm. and w (omega)=2*pi*f, 2*4.5*pi=9pi radians/second
Title: Re: Physics help!
Post by: nid404 on August 26, 2010, 02:17:24 pm: Ahhh....ohkay that way...thanks dude..+rep :)
Title: Re: Physics help!
Post by: cooldude on August 26, 2010, 02:20:13 pm: Quote from: ~Ahana~ on August 26, 2010, 02:17:24 pm
Ahhh....ohkay that way...thanks dude..+rep :)

oh yeah and one more thing, u can also tell its starts from the maximum position cuz its a function of cos and not sine, and Thanks for the rep ;D
Title: Re: Physics help!
Post by: nid404 on August 26, 2010, 02:59:13 pm: yeah I figured that....didn't really notice what they were asking for. :-[

Ah...one more question

June 2010 paper 4 variant 1, Q3 b) How can they say acceleration is constant ? :S Is it because a=g ? :-\
Title: Re: Physics help!
Post by: cooldude on August 26, 2010, 03:29:04 pm: Quote from: ~Ahana~ on August 26, 2010, 02:59:13 pm
yeah I figured that....didn't really notice what they were asking for. :-[

Ah...one more question

June 2010 paper 4 variant 1, Q3 b) How can they say acceleration is constant ? :S Is it because a=g ? :-\

yeah in a way, well the component of the weight that acts down is mgsinx, let x be the angle between the inclined plane and the ground, so mgsinx=ma
so a=gsinx, x is the same for both and g is a constant therefore the acceleration is constant and therefore it cant be shm as a varies with the displacement
Title: Re: Physics help!
Post by: nid404 on August 26, 2010, 03:30:14 pm: yup component of g I meant...ohk just confirming...thanks :)
Title: Re: Physics help!
Post by: nid404 on September 10, 2010, 04:49:19 pm: With reference to capacitors, can someone explain what 'smoothing' is?
Title: Re: Physics help!
Post by: M-H on September 10, 2010, 09:57:38 pm: Yeah capacitors smoothen AC. As in think of it, the capacitor is charged during the positive cycle, while it discharges during the negative cycle. the discharging and charging takes up time...that way, the discharging and charging do not happen at equal intervals..eventually, a graph that would be normally with distinct waves, with a capacitor, you can see it becoming for even.

Sorry, this is a rough explanation. hope it helped.
Title: Re: Physics help!
Post by: nid404 on September 11, 2010, 06:09:57 am: Uhm...Can you get me a graph please ;D Visualizing this is beyond the capacity of my cat brain :P Physics doesn't go well with me ::)
Title: Re: Physics help!
Post by: nid404 on September 11, 2010, 06:57:50 am: And yes Where can I find notes on Application of Physics?

I DO HAVE the CIE Application Booklet for reference(which is pretty useless)

Thank you
Title: Re: Physics help!
Post by: M-H on September 11, 2010, 09:31:56 am: i'll try to get you sth!! haha, its okay! cat brains :P

Hey, what i usually do for finding out about the applications- i look it up on wikipedia!
Like for capacitors, one important application is, charged coupled devies...so just find out and they explain how the actual thing happens!
Title: Re: Physics help!
Post by: nid404 on September 11, 2010, 10:18:12 am: Wikipedia ahan...okay I'll go through..thanks :)
Title: Re: Physics help!
Post by: M-H on September 11, 2010, 01:30:36 pm: http://www.kpsec.freeuk.com/powersup.htm#smoothing
Title: Re: Physics help!
Post by: M-H on September 11, 2010, 01:38:13 pm: Hey, the only difference between the things mentioned in the link i provided and AC, is, that AC have both negative and positive cycles. During the positive cycle, a capacitor is charged, but during the negative, it discharges.
Title: Re: Physics help!
Post by: nid404 on September 11, 2010, 01:45:10 pm: Well smoothing is the same as having a rectifier with capacitor filter right?
Title: Re: Physics help!
Post by: M-H on September 11, 2010, 02:03:23 pm: No a rectifier would cut the negative cycles. Its the time that's taken up by the discharging and charging that makes the time interval different, and therefore, your wave is not the same as before. it would become less steep. Eventually, by becoming more and more shallow, its becoming smooth and even!
Title: Re: Physics help!
Post by: nid404 on September 11, 2010, 02:08:36 pm: Uhm...if it's an alternating current, the graph would be different. The graph you showed me is one with a full wave rectifier and a capacitor filter.
Title: Re: Physics help!
Post by: M-H on September 11, 2010, 10:40:19 pm: Urgh...i...

Alright..i'll look for something to explain my bit hopefully soon!
Title: Re: Physics help!
Post by: nid404 on September 12, 2010, 04:54:04 pm: I've figured it...thanks for your help though :)
Title: Re: Physics help!
Post by: M-H on September 12, 2010, 09:39:35 pm: Phew! :)
Title: Re: Physics help!
Post by: nid404 on September 14, 2010, 04:42:14 pm: Not yet :P

Can someone explain this BS =.=

Thank you
Title: Re: Physics help!
Post by: Deadly_king on September 15, 2010, 05:47:24 am: Quote from: Garfield on September 14, 2010, 04:42:14 pm
Not yet :P

Can someone explain this BS =.=

Thank you

Answers for V_out will be as follows : 1 2 4 5 6 7

I'll explain now..........in the first row
V_A = 0, V_B = 0 and V_C = 1. Hence resulting V_out was given to be 1V.
In other words he meant that when V_C = 1 ------> V_out = 2⁰ = 1

For the 2^nd row
Only V_A = 1. the others were zero and the value for V_out was given to be 4V.
Therefore when V_A = 1 ------> V_out= 2² = 4V

Everything is in powers of two.

When any voltage is given to be zero.........it is indeed zero.

When V_A = 1 --------> 2²V
When V_B= 1 --------> 2¹V
When V_C = 1 --------> 2⁰V

For V_out, you just have to add the values of V_A,V_B and V_C

The fifth row : V_out = 2² + 2¹ + 0 = 6V
The sixth row : V_out = 2² + 2¹ + 2⁰ = 7V

Hope it helps :)
Title: Re: Physics help!
Post by: nid404 on September 19, 2010, 08:33:39 am: Thank youuuuuuuu + rep
Title: gravitaional ques!!
Post by: sizbeauty on September 19, 2010, 04:58:15 pm: a space capsule is travelling b/w the earth n moon.find the distance frm the earth at which it is subjct to zero gravitational force??
(mass of the earth: 6.0*10^24,mass of moon: 7.4*10^22,this b/w the centres of earth n moon:3.8*10^8)
plz help me out in this ques!!
Title: Re: gravitaional ques!!
Post by: nid404 on September 19, 2010, 05:15:22 pm: Quote from: sizbeauty on September 19, 2010, 04:58:15 pm
a space capsule is travelling b/w the earth n moon.find the distance frm the earth at which it is subjct to zero gravitational force??
(mass of the earth: 6.0*10^24,mass of moon: 7.4*10^22,this b/w the centres of earth n moon:3.8*10^8)
plz help me out in this ques!!

The gravitation pull of the earth should match the gravitational pull of moon.

F=Gm1m2/ r²

GX 6.0*10^24m2/r²= G X 7.4*10^22m2/ (3.8*10^8-r)²

Solve for r
Title: Re: Physics help!
Post by: elemis on September 19, 2010, 05:18:18 pm: I would so love to understand all of that one day. :-\
Title: Re: Physics help!
Post by: nid404 on September 19, 2010, 05:19:13 pm: Quote from: Ari Ben Canaan on September 19, 2010, 05:18:18 pm
I would so love to understand all of that one day. :-\

Me too ::)
Title: Re: Physics help!
Post by: elemis on September 19, 2010, 05:23:30 pm: Quote from: Garfield on September 19, 2010, 05:19:13 pm
Me too ::)

JOKE OF THE MILLENNIUM !!! :D

EPIC !!! :D
Title: Re: Physics help!
Post by: nid404 on September 19, 2010, 05:27:56 pm: Quote from: Ari Ben Canaan on September 19, 2010, 05:23:30 pm
JOKE OF THE MILLENNIUM !!! :D

EPIC !!! :D

Yeah laugh ::)
Title: Re: Physics help!
Post by: elemis on September 19, 2010, 05:34:58 pm: Quote from: Garfield on September 19, 2010, 05:27:56 pm
Yeah laugh ::)

You're serious ? :o
Title: Re: Physics help!
Post by: nid404 on September 19, 2010, 05:35:34 pm: Quote from: Ari Ben Canaan on September 19, 2010, 05:34:58 pm
You're serious ? :o

Shaap :P
Title: Re: Physics help!
Post by: elemis on September 19, 2010, 05:39:43 pm: Quote from: Garfield on September 19, 2010, 05:35:34 pm
Shaap :P

up shut :P
Title: Re: Physics help!
Post by: sizbeauty on September 19, 2010, 06:11:05 pm: hey i m getting R=3.4*10^9 but in pstpprz ans is R=3.4*10^8...cn u plz c where am i going wrong??
n scndly,i gt tht u cancelld out value of G on both sidez but wht abt m2?? why did u cancel it out??
bdw thanx alot!! :) :)
Title: Re: Physics help!
Post by: nid404 on September 19, 2010, 06:14:50 pm: m2 is the same on either sides so they get cancelled too.

The answer can't be 10^9 because the distance between the earth and moon itself is to the power 10^8. Check the numbers again.
Title: Re: Physics help!
Post by: sizbeauty on September 19, 2010, 06:24:09 pm: yeah i got the correct ans!! ;D
bdw whose mass basically is m2?? ???
Title: Re: Physics help!
Post by: nid404 on September 19, 2010, 06:26:36 pm: The space capsule. ;D
Title: Re: Physics help!
Post by: sizbeauty on September 19, 2010, 06:28:41 pm: oooh stupid me!! ;D
thankU!! :)
Title: Re: Physics help!
Post by: nid404 on September 23, 2010, 06:50:31 pm: Anytime :)
Title: Re: Physics help!
Post by: $!$RatJumper$!$ on October 01, 2010, 10:22:47 am: Hi guys.. a quick question.

For AS level physics, the syllabus mentions we should be able to "make reasonable estimates of physical quantities included within the syllabus". The thing is i ALWAYS struggle in making estimates in paper 2. Is there any place i can get some notes, or tips on how to tackle those types of questions?
Also, since it says "physical quantities included within the syllabus", where are these quantities listed in the syllabus?
Title: Re: Physics help!
Post by: Deadly_king on October 02, 2010, 08:12:41 am: Quote from: $!$RatJumper$!$ on October 01, 2010, 10:22:47 am
Hi guys.. a quick question.

For AS level physics, the syllabus mentions we should be able to "make reasonable estimates of physical quantities included within the syllabus". The thing is i ALWAYS struggle in making estimates in paper 2. Is there any place i can get some notes, or tips on how to tackle those types of questions?
Also, since it says "physical quantities included within the syllabus", where are these quantities listed in the syllabus?

Sorry I cannot really help you there since I don't know any such sites.

The physical quantities however are all the base units that you need to know like mass, length, current, temperature etc...

It's not really listed.........but it includes any quantity that you came across throughout the syllabus. ;)
Title: Re: Physics help!
Post by: $!$RatJumper$!$ on October 02, 2010, 04:10:43 pm: Thankx dude :)
Title: Re: Physics help!
Post by: Deadly_king on October 02, 2010, 04:13:33 pm: Quote from: $!$RatJumper$!$ on October 02, 2010, 04:10:43 pm
Thankx dude :)
Anytime man :)