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

Qualification => GCE O - Level => Queries => Topic started by: astarmathsandphysics on October 06, 2008, 11:00:30 am

Title: Maths & Physics Help
Post by: astarmathsandphysics on October 06, 2008, 11:00:30 am: Post your O Level questions here to get the answers back asap from someone with 3 maths/physics degrees.
Title: Re: Maths & Physics Help
Post by: justx007 on January 18, 2009, 03:38:14 pm: Why does a car brak system use oil whereas for lorries, some uses air ?
Title: Re: Maths & Physics Help
Post by: astarmathsandphysics on January 18, 2009, 09:36:15 pm: think it is because a truck can use it's own weight - up to 40 tonnes - to compress the air that applies the braking force. A car weighs 2 tonnes max, so they have touse oil, which is virtually incompressible. That way, the braking is instant. I will check with a mechanic I know.
Title: Re: Maths & Physics Help
Post by: astarmathsandphysics on January 18, 2009, 10:17:25 pm: I have been told this by my mechanic friend

Normal car brakes operate by using pressure to apply the brakes, but if you somehow lose your brake fluid, you lose all braking. This is why some trucks have the opposite. The reasoning behind this is that if you blow an air line or lose pressure to the brakes, the brakes will apply and stop the truck. They won't come off again until they are pressurised. It's more of a safety factor... I don't like the idea of a truck with no brakes.
Title: Re: Maths & Physics Help
Post by: Amna M. on March 14, 2009, 01:24:51 pm: How can I get good at vectors? I've revised the topic a million times and practised every question I found, but I've only improved a little!
Title: Re: Maths & Physics Help
Post by: astarmathsandphysics on March 14, 2009, 01:30:50 pm: I think there are only five types of question they can ask. It shouldn't be too hard to learn them all. Shall I do some specimen answers/solutions? Or you could post some questions here.
Title: Re: Maths & Physics Help
Post by: saifalan on March 14, 2009, 02:48:30 pm: Plz dnt mind me asking, wht kind of student r u ?? I mean r u an average or above average. Give us an example of ur avrge percentages. Vectors in O levels arent that hard, heck it aint tht hard in Alevels. May be u tend to memorize maths than understand it, which I used to do. So u cant be better when u do that. Think carefully where u r going wrong.
Title: Re: Maths & Physics Help
Post by: Pharoah on May 08, 2009, 10:50:49 am: Why does a car move forward when the friction on the tires is forward and the driving force backwards?
Title: Re: Maths & Physics Help
Post by: astarmathsandphysics on May 08, 2009, 10:55:45 am: Quote from: Pharoah on May 08, 2009, 10:50:49 am
Why does a car move forward when the friction on the tires is forward and the driving force backwards?

The friction force is ALWAYS against the direction of motion. If the driving force it backwards it does not mean the car is moving nackwards only that the acceleration is backwards.
Title: Re: Maths & Physics Help
Post by: Pharoah on May 08, 2009, 11:04:59 am: But if the acceleration is backwards shouldn't the car move backwards too? I don't understand.. ???
Title: Re: Maths & Physics Help
Post by: astarmathsandphysics on May 08, 2009, 11:06:51 am: The car can be moving forward but slowing down which is accelerating backwards. The driving for can be forwards, and friction is always against the direction of motion.
Title: Re: Maths & Physics Help
Post by: Pharoah on May 08, 2009, 11:12:07 am: But isn't friction always forward in tyres? Ok I think I get it. If the driving force is forwards, both forces will be added to give acceleration. Am I right?
Title: Re: Maths & Physics Help
Post by: astarmathsandphysics on May 08, 2009, 11:15:35 am: If both forces are backwards, it probably means the brakes are applied. Then the forces are added.
I the engine is moving the car forward and thwe car is slowing down then the friction force is bigger than the engines force.
Title: Need help in additional maths.
Post by: nox_fjmoony on June 21, 2009, 07:32:31 am: Hey, I was practising add maths from the qp and well I kinda got stuck. Its no 11 OR from the o/n-07 paper 1 add maths qp. Its the CIE one. Thanks in advance. :D
Title: Re: Need help in additional maths.
Post by: astarmathsandphysics on June 21, 2009, 09:09:28 am: Quote from: nox_fjmoony on June 21, 2009, 07:32:31 am
Hey, I was practising add maths from the qp and well I kinda got stuck. Its no 11 OR from the o/n-07 paper 1 add maths qp. Its the CIE one. Thanks in advance. :D

i) $\frac{d}{dx}\frac{lnx}{x^2}=\frac{x^2*1/x-2xlnx}{x^4}=\frac{x-2xlnx}{x^4}=\frac{1-2lnx}{x^3}$

ii)Stationary point is where $\frac{dy}{dx}=0$
$\frac{1-2lnx}{x^3}=0$ so $1-2lnx=0$ so $x=e^{1/2}$ then $y=\frac{lnx}{x^2}=\frac{1/2}{(e^{1/2})^2}=\frac{1}{2e}$

iii)rearrange $\frac{d}{dx}\frac{lnx}{x^2}=\frac{1-2lnx}{x^3}$ to make $\frac{lnx}{x^3}$ the subject

$\frac{lnx}{x^3}=\frac{1}{2x^3}-\frac{d}{dx}\frac{lnx}{x^2}$ Then integrate to get

$-\frac{1}{4x^2}-\frac{lnx}{x^2}+C$
Title: Re: Need help in additional maths.
Post by: nox_fjmoony on June 21, 2009, 12:46:20 pm: hey thanks Astar.
But you see its where the e part that I don't understand. I'm just starting add maths for the october november session and well I really don't understand how to get the e thingy.
And thanks a lot again.
^_^
Title: Re: Need help in additional maths.
Post by: astarmathsandphysics on June 21, 2009, 01:05:29 pm: I edited my post to make it clearer.

To solve the equation y=log_nx raise the base to the power of both side so n^y=x
Title: Re: Need help in additional maths.
Post by: astarmathsandphysics on June 21, 2009, 01:10:40 pm: ln x is special notation for log_nx=lnx
Title: Re: Need help in additional maths.
Post by: nox_fjmoony on June 21, 2009, 03:06:00 pm: thanks
but
I have a problem in another part
The part where it becomes x=e^1/2 all of a sudden. I'm quite outta practice and so don't quite understand it. Didn't understand that part in the mark scheme either.

Also whats the relationship between ln and e please?
Thankyou very very much Astar. ^_^

Really grateful.
:D
Title: Re: Need help in additional maths.
Post by: astarmathsandphysics on June 21, 2009, 03:43:42 pm: $2lnx=1$ so lnx=1/2 so $e^{lnx}=e^{1/2}$ so $x=e^{1/2}$
Title: Re: Need help in additional maths.
Post by: nox_fjmoony on June 21, 2009, 04:52:02 pm: Ok
Another question
I guess by this time you might've guessed I"m absolutely stupid and a dunce. But I have to know this.
ok so how does lnx=1/2 becomes e^lnx=e^1/2 ?
I don't know this.
what do you do to make it like this?

I'm sorry but as you see I don't know much about ln and log and e and stuff.
Ok thanks again.
Title: Re: Need help in additional maths.
Post by: astarmathsandphysics on June 21, 2009, 05:53:21 pm: To eliminate a log you raise the base to the power of both sides. Here the base is e=2.718.........
Title: Re: Need help in additional maths.
Post by: nox_fjmoony on June 22, 2009, 04:10:25 pm: Ah
Finally
I get it. Thanks so much, wouldn't have known this without you tellin me.
Thanks again.
;D
Title: Re: Need help in additional maths.
Post by: nox_fjmoony on June 23, 2009, 01:51:54 pm: hey astar
Another question. Um how does e^lnx=e^1/2 become x=e^1/2 later on?
ok
thanks
Title: Re: Need help in additional maths.
Post by: astarmathsandphysics on June 23, 2009, 01:54:25 pm: Quote from: nox_fjmoony on June 23, 2009, 01:51:54 pm
hey astar
Another question. Um how does e^lnx=e^1/2 become x=e^1/2 later on?
ok
thanks

e^ cancels log_e=ln

ln is special notation for log_e
Title: Re: Maths & Physics Help
Post by: nid404 on September 26, 2009, 06:30:50 pm: Sir, do you notes on your site for complex numbers??
Title: Re: Maths & Physics Help
Post by: holtadit on October 20, 2009, 02:35:47 pm: https://studentforums.biz/index.php/topic,4384.0.html

Please look at my post which the link leads to..
Title: Re: Maths & Physics Help
Post by: toobeerajpanchoo on October 24, 2009, 11:57:10 am: hi help in maths of cie
could u please provide me formula of how to calculate interior or exterior angle of a regular polygon and also how to calculate on kinematics PLEASE SOME OTHER ALSO FORMULAS USED IN MATHEMATICS THANKS :-[
Title: Re: Maths & Physics Help
Post by: Ghost Of Highbury on October 24, 2009, 12:09:07 pm: Quote from: toobeerajpanchoo on October 24, 2009, 11:57:10 am
hi help in maths of cie
could u please provide me formula of how to calculate interior or exterior angle of a regular polygon and also how to calculate on kinematics PLEASE SOME OTHER ALSO FORMULAS USED IN MATHEMATICS THANKS :-[

if n=number of sides

interior angle = ((n-2)*180)/n

which kinematics formula u want exactly?

v=u + at
s = ut + 0.5at²

v² = u² + 2as

s = (u+v)t/2
Title: Re: Maths & Physics Help
Post by: wassup on October 24, 2009, 12:09:47 pm: Quote from: toobeerajpanchoo on October 24, 2009, 11:57:10 am
hi help in maths of cie
could u please provide me formula of how to calculate interior or exterior angle of a regular polygon and also how to calculate on kinematics PLEASE SOME OTHER ALSO FORMULAS USED IN MATHEMATICS THANKS :-[

n=No. of sides

Sum of interior angles=180(n-2)

One interior angle=Sum of interior angles/n

One exterior angle=180^o-One interior angle
Title: Re: Maths & Physics Help
Post by: toobeerajpanchoo on October 24, 2009, 12:15:17 pm: HEY | am | I WANNA KNOW HOW U DO TO CALCULATE AREA UNDER GRAPH ALL ITS FORMULAS
Title: Re: Maths & Physics Help
Post by: Ghost Of Highbury on October 24, 2009, 12:23:07 pm: Quote from: toobeerajpanchoo on October 24, 2009, 12:15:17 pm
HEY | am | I WANNA KNOW HOW U DO TO CALCULATE AREA UNDER GRAPH ALL ITS FORMULAS

if its a speed-time graph...the area under the graph would be the distance covered.

Theres no formula to find it, u have to first identify the shape. It can be a trapezium/square/triangle anything..

find a sample graph below and i have shown how u calculate the area under the graph..

----

first identify the shape - trapezium

area of trapezium = 0.5 * (sum of parallel sides) * perpendicuar height = 0.5 * (7+10) * 25 = 212.5cm²

--

u can also use integration to find the area.
Title: Re: Maths & Physics Help
Post by: toobeerajpanchoo on October 24, 2009, 01:03:22 pm: ALRIGHT I UNDERSTOOD BUT COULD EXPLAIN HOW TO DO THE QUESTIONS IN JUNE 2008 CIE ABOUT KINEMATICS PAPER 1
Title: Re: Maths & Physics Help
Post by: astarmathsandphysics on October 24, 2009, 01:12:57 pm: which question?
Title: Re: Maths & Physics Help
Post by: toobeerajpanchoo on October 24, 2009, 01:29:31 pm: NO 13
13 The diagram is the speed-time graph of the first 20 seconds of a motorcyclist’s journey.
Speed
(a) Calculate the motorcyclist’s retardation during the final 8 seconds.
(b) Calculate the distance travelled in the 20 seconds.
Title: Re: Maths & Physics Help
Post by: astarmathsandphysics on October 24, 2009, 02:49:12 pm: Will answer when i get home
Title: Re: Maths & Physics Help
Post by: Ghost Of Highbury on October 24, 2009, 03:10:49 pm: Quote from: toobeerajpanchoo on October 24, 2009, 01:29:31 pm
NO 13
13 The diagram is the speed-time graph of the first 20 seconds of a motorcyclist’s journey.
Speed
(a) Calculate the motorcyclist’s retardation during the final 8 seconds.
(b) Calculate the distance travelled in the 20 seconds.

use the formula

v = u+at

s=ut + 0.5at²
Title: Re: Maths & Physics Help
Post by: toobeerajpanchoo on October 24, 2009, 03:27:50 pm: ALRIGHT :)
Title: Re: Maths & Physics Help
Post by: astarmathsandphysics on October 24, 2009, 04:59:51 pm: a)The final 8 seconds is a triangle base 8 height 30
area= 0.5bh=0.5*8*30=120m
b) cut up the first 12s into a triangle base 8 and height 15 so area =0.5*8*15=60
and trpezium a=15 b=30 h=4
0.5(a+b)h =0.5*(15+30)4=90
total area =60+90+120=270m
Title: Re: Maths & Physics Help
Post by: sasukeuchiha on May 25, 2010, 04:29:22 pm: please give me the answer of o levels physics October/November 2008 mcq paper 1 question no. 23
please give an explanation too
http://www.freeexampapers.com/FreeExamPapers.com_.php?__lo=TyBMZXZlbC9QaHlzaWNzL0NJRS8yMDA4IE5vdi81MDU0X3cwOF9xcF8xLnBkZg== (http://www.freeexampapers.com/FreeExamPapers.com_.php?__lo=TyBMZXZlbC9QaHlzaWNzL0NJRS8yMDA4IE5vdi81MDU0X3cwOF9xcF8xLnBkZg==)
Title: Re: Maths & Physics Help
Post by: DrEvil on May 25, 2010, 06:59:17 pm: Quote from: sasukeuchiha on May 25, 2010, 04:29:22 pm
please give me the answer of o levels physics October/November 2008 mcq paper 1 question no. 23
please give an explanation too
http://www.freeexampapers.com/FreeExamPapers.com_.php?__lo=TyBMZXZlbC9QaHlzaWNzL0NJRS8yMDA4IE5vdi81MDU0X3cwOF9xcF8xLnBkZg== (http://www.freeexampapers.com/FreeExamPapers.com_.php?__lo=TyBMZXZlbC9QaHlzaWNzL0NJRS8yMDA4IE5vdi81MDU0X3cwOF9xcF8xLnBkZg==)

The answer is C. Extend the rays beyond the mirror that are entering the eye and you'll get the explanation.
Title: Re: Maths & Physics Help
Post by: sasukeuchiha on May 25, 2010, 09:20:07 pm: many thanks :)..that was a concept left to be cleared
Title: Re: Maths & Physics Help
Post by: DrEvil on May 25, 2010, 09:33:17 pm: Quote from: sasukeuchiha on May 25, 2010, 09:20:07 pm
many thanks :)..that was a concept left to be cleared

my pleasure.. 8)