Author Topic: Maths/Physics help  (Read 20355 times)

Offline astarmathsandphysics

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Maths/Physics help
« on: October 06, 2008, 10:59:23 am »
Post your IB questions here to get the answers back asap from someone with 3 maths/physics degrees.

Offline milton

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Re: Maths/Physics help
« Reply #1 on: November 18, 2008, 02:35:55 pm »
Whats the formula/method for perpendicular distance of a point to a plane?

Offline astarmathsandphysics

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Re: Maths/Physics help
« Reply #2 on: November 19, 2008, 09:47:59 am »
I will give an example. Point(2,3,1) and plane 9x+8y+7z=4.

The equation of the line from the point to the plane is r=(2,3,1)+t(9,8,7)
so for this line x=2+9t
                       y=3+8t
                       z=1+7t
Substitute these into equation of plane

9(2+9t)+8(3+8t)+7(1+7t)=4
49+194t=4 so t=-45/194
and r intersects the plane at the point (2,3,1)-45/194(9,8,7)=(-17/194,222/194,-121/194)

Now find the distance between (2,3,1) and the point just found using the formula sqrt((x1-x2)^2+(y1-y2)^2+(z1-z2)^2)

Offline milton

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Re: Maths/Physics help
« Reply #3 on: November 20, 2008, 09:38:24 am »
My memory is sketchy, but I found a tough question, worth 15 marks.

Serious car accidents on a road follow a Poisson distribution and have a mean of 2 per week.

a) What is the mean in a 4-week period

b) Given that 1 year has 13 four-week periods, what is the probability of nine of those 13 four-week periods having atleast 1 serious car accidents

c) If the probability of a car crash in 'n' weeks is 0.99, what is n

Offline astarmathsandphysics

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Re: Maths/Physics help
« Reply #4 on: November 20, 2008, 09:52:19 am »
My memory is sketchy, but I found a tough question, worth 15 marks.

Serious car accidents on a road follow a Poisson distribution and have a mean of 2 per week.

a) What is the mean in a 4-week period

b) Given that 1 year has 13 four-week periods, what is the probability of nine of those 13 four-week periods having atleast 1 serious car accidents

c) If the probability of a car crash in 'n' weeks is 0.99, what is n

a)8
b)The poisson is scalable so the probability distribution now is Po(eight) so P(X=k)=e^-8*8/k!. the probability that x>=1 accident in 1 month is 1-e^-8*8^0/0!=1-e^-8
Now we have a binomial B(13,8e^-1) so P(x=9)=13!/(4!9!)*(e^-8)^4(1-(e^-8))^9

C) The probability of a no car crashese is 1-e^-2
So solve 0.01=(1-e^-2)^n

n=ln(0.01)/ln(1-e^-2)
« Last Edit: November 20, 2008, 10:09:03 am by astarmathsandphysics »

Offline omarsubei

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Math Conversion Question
« Reply #5 on: November 22, 2008, 05:05:59 pm »
Hi, I'd be grateful if you can tell me how to convert metres per minute squared (acceleration) to feet per second squared (also acceleration) and vice versa. I just can't do it!!! Thanks

Offline astarmathsandphysics

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Re: Math Conversion Question
« Reply #6 on: November 22, 2008, 05:10:18 pm »
Hi, I'd be grateful if you can tell me how to convert metres per minute squared (acceleration) to feet per second squared (also acceleration) and vice versa. I just can't do it!!! Thanks


Divide by 3600 to change meters per minute squared into meters per second squared then Times by 3.3 since there are 3.3 feet in every meter

Offline omarsubei

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Re: Maths/Physics help
« Reply #7 on: November 22, 2008, 05:14:23 pm »
Thanks a LOT. Wow, you're quite fast at responding.

Offline lolo

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Re: Maths/Physics help
« Reply #8 on: February 01, 2009, 09:30:00 am »
heyy am still stuck in vectors
i dont get it  ???
so if i have a question like this how do i solve it?
pointA and B have coordinates (4, 1) and (2, -5), respectively. Find a vector equation for the line which passes through the point A, and which is perpendicular to the line AB.

really appreaciate ur help
thanks :)

Offline astarmathsandphysics

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Re: Maths/Physics help
« Reply #9 on: February 01, 2009, 01:25:22 pm »
heyy am still stuck in vectors
i dont get it  ???
so if i have a question like this how do i solve it?
pointA and B have coordinates (4, 1) and (2, -5), respectively. Find a vector equation for the line which passes through the point A, and which is perpendicular to the line AB.

really appreaciate ur help
thanks :)


gradient of line from A to B =change in y/change in x=(-5-1)/(2-4)=3 so gradient of perpendicular =-1/3

y=mx+c

y=-1/3x+c Put point A in to this equation.
1=(_1/3)4+c
so c=7/3 and y=-1/3x+7/3

Offline lolo

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Re: Maths/Physics help
« Reply #10 on: February 01, 2009, 02:01:16 pm »
wooww!! omg i actually get it nw!! :D
u r smart lol

thankooo soooo much :D
really appreciate it ..
:)

Offline astarmathsandphysics

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Re: Maths/Physics help
« Reply #11 on: February 01, 2009, 02:11:18 pm »
Thanks. Post all your maths questions.

Offline saifalan

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Re: Maths/Physics help
« Reply #12 on: February 01, 2009, 03:32:16 pm »
Good way to learn maths. But, alas, there isnt a good way to write down all the mathematical notations down
Why so seroisee ??

Offline astarmathsandphysics

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Re: Maths/Physics help
« Reply #13 on: February 01, 2009, 09:07:00 pm »
There is - we have latex now. Look at the pi button- that is the latex code thingy, but I dont know how to use it yet.

Offline saifalan

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Re: Maths/Physics help
« Reply #14 on: February 02, 2009, 01:05:05 pm »
 ;D if u havnt found a way to use it yet, it is as well as not there.
Why so seroisee ??