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Author Topic: Maths & Physics Help  (Read 17824 times)

Offline astarmathsandphysics

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Maths & Physics Help
« 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.
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Offline justx007

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Re: Maths & Physics Help
« Reply #1 on: January 18, 2009, 03:38:14 pm »
Why does a car brak system use oil  whereas for lorries, some uses  air ?
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Offline astarmathsandphysics

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Re: Maths & Physics Help
« Reply #2 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.
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Offline astarmathsandphysics

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Re: Maths & Physics Help
« Reply #3 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.
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Offline Amna M.

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Re: Maths & Physics Help
« Reply #4 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!
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Offline astarmathsandphysics

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Re: Maths & Physics Help
« Reply #5 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.
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Offline saifalan

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Re: Maths & Physics Help
« Reply #6 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.
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Offline Pharoah

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Re: Maths & Physics Help
« Reply #7 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?
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Offline astarmathsandphysics

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Re: Maths & Physics Help
« Reply #8 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.
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Offline Pharoah

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Re: Maths & Physics Help
« Reply #9 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..  ???
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Offline astarmathsandphysics

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Re: Maths & Physics Help
« Reply #10 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.
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Offline Pharoah

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Re: Maths & Physics Help
« Reply #11 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?
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Offline astarmathsandphysics

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Re: Maths & Physics Help
« Reply #12 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.
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Offline nox_fjmoony

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Need help in additional maths.
« Reply #13 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
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Offline astarmathsandphysics

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Re: Need help in additional maths.
« Reply #14 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
« Last Edit: June 21, 2009, 01:03:41 pm by astarmathsandphysics »
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