Chopsen, you are brilliant! 
Maths Help! • Page 3

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White_Shadow 2,538 posts
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Dangerous_Dan 2,390 posts
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Registered 7 years ago@White_Shadow With your provided numbers I come up with about 1323.13 people who visited both displays. This assumes that there's nobody who visited neither of the displays. If you assume that some people stayed away from both displays then there is not enough information provided to calculate the exact number but an interval can be calculated.
Damn Sir Chopsen was faster!
Edited by Dangerous_Dan at 23:14:45 24102012 
sensoji 7,884 posts
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Registered 9 years agoI have a mechanics maths problem if anyone cares to help:
Assume a sprinter runs 100m in 9.83 seconds. He accelerates constantly for the first 60m and then runs at his maximum speed for the remaining 40m.
Calculate:
A  The maximum speed
B  The acceleration
This is an actual exam question I've seen and I'm flumoxed as to how to work it out. I know all the motion in a straight line formulas but can't seem to work out how to use them to get both those answers. 
dominalien 8,206 posts
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Registered 11 years agoNo, not 40% of the time, just 40% of the distance. 
Saucy 2,729 posts
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Registered 7 years agoIf his maximum speed is A m/s, then he covers 40% of the course at speed A, and 60% and 1/2 A (constant acceleration). So I reckon,
Average Speed = 0.4*A + 0.6*1/2 A
100/9.83= 0.7 A
A = 100/(9.83*0.7)
Can't remember straight line formulae I'm afraid, but think acceleration should be fairly simple from here. 
X201 17,961 posts
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warlockuk 19,389 posts
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Registered 13 years agosensoji wrote:
Interesting.
I have a mechanics maths problem if anyone cares to help:
Assume a sprinter runs 100m in 9.83 seconds. He accelerates constantly for the first 60m and then runs at his maximum speed for the remaining 40m.
Calculate:
A  The maximum speed
B  The acceleration
This is an actual exam question I've seen and I'm flumoxed as to how to work it out. I know all the motion in a straight line formulas but can't seem to work out how to use them to get both those answers.
Spent ages trying to work this out, think I'm missing something 
warlockuk 19,389 posts
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Registered 13 years agoOh wait, it's easy.
His constant acceleration as someone said means he averages half the final speed in the first 60metres
So 60 metres at v/2 + 40m at v
or if it was equal, 120m at v and 40m at v would mean at the actual speed he would've covered 160, not 100 metres.
So, 160/9.83 = 16.27670397 for his final speed.
At that speed, the 40 metres end piece would take 2.4575 seconds leaving 7.3725 seconds to accellerate to 16.27670397 m/s
Acceleration is finalvel  start vel / time
16.27670397 / 7.3725 = 2.2077591 metres per second per second.
So (Fixed as I put A+B in the wrong order originally)
A: 16.27670397 m/s for the final top speed
B: 2.2077591 m/s/s for the initial acceleration
Edited by warlockuk at 12:06:12 25102012 
Alastair 20,257 posts
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Registered 15 years agoWhat level of maths are we talking? GCSE or Alevel?
Somehow I wonder if this is related to integrating/differentiating wrt time or summat. 
warlockuk 19,389 posts
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Registered 13 years agoChecks out, too.
Acceleration at (B) for 7.3725 seconds = (B*T^2) / 2 = 60 metres
Velocity = (B) * (T) = A \o/ Qapla' !
*edit fixed for answering A+B the wrong way round before
Edited by warlockuk at 12:04:02 25102012 
warlockuk 19,389 posts
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Registered 13 years agoAlastair wrote:
I think it's technically Alevel but once you realise it's a straightline and geometry (mentally) fits in you can squeeze it into GCSE maths or Physics.
What level of maths are we talking? GCSE or Alevel?
Somehow I wonder if this is related to integrating/differentiating wrt time or summat. 
mal 27,720 posts
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Registered 15 years agoSaucyGeoff wrote:
I think you've made the mistake dominalien pointed out  that you've averaged the speed assuming he spent 60% of his time accelerating, rather than 60% of the distance (or 60m in this example).
If his maximum speed is A m/s, then he covers 40% of the course at speed A, and 60% and 1/2 A (constant acceleration). So I reckon,
Average Speed = 0.4*A + 0.6*1/2 A
100/9.83= 0.7 A
A = 100/(9.83*0.7)
Can't remember straight line formulae I'm afraid, but think acceleration should be fairly simple from here.
Using the formula:
speed = distance/time then
distance = time * speed
Also, distance = time * average speed for varying speeds
So 40 = b * n and 60 = a * n/2 where a and b are the times taken and n the the maximum speed
Rearrange those expressions to express a and b in terms of n, then replace them in the time equation (a+b=9.87). Therefore you have an expression with just n as a variable.
Converting that to acceleration means you need to know how long he spent accelerating. That's a, which now you know n you can work out. Working out the actual acceleration from there is left as an exercise to the reader (mainly because I've forgotten all my acceleration formulas).
Edit: Yeah, warlock got it
Edited by mal at 12:05:06 25102012 
speedofthepuma 13,399 posts
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Registered 11 years agoGod damn we are a sexy bunch! 
warlockuk 19,389 posts
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Registered 13 years agoStop fapping over my profile picture. 
Saucy 2,729 posts
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Registered 7 years ago@mal Ah, I see. Rookie mistake. I remember doing this kind of question during ALevels. Used to know all these formulae! 
neilka 20,012 posts
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Registered 12 years agoIs the sprinter on a treadmill wearing a spacesuit? 
Alastair 20,257 posts
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Registered 15 years agoneilka wrote:
Only when Lutz is answering...
Is the sprinter on a treadmill wearing a spacesuit? 
sensoji 7,884 posts
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Registered 9 years agoThanks guys  Warlockuk got the answer right
The question is from Alevel maths Mechanics 1 module. 
boo 13,124 posts
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Registered 14 years agoI'm ashamed at how rusty I've become regarding maths.
This was a puzzle I saw the other day, and while I have the answer, I can't get my head around the 'x cancels out' bit. Can anyone clarify for me.
Original puzzle is:
Rich person decides to give £45 to each man and £60 to each woman.
Only 1/9th of men claim their prize.
Only 1/12th of women claim their prize.
There are 3552 people who can claim.
How much is paid out?
Solution.
If there are x men, then there must be (3552x) women.
(x/9) received £45
((3552x) / 12) received £60
Total paid = (45 * (x/9)) + (60 * (3552x) / 12)
x cancels out, leaving
5 * 3552 = 17,760
How does x cancel out? If you add x to the right hand side of the equation, that would leave
(45 * (x/9)) + x
/is baffled 
Dangerous_Dan 2,390 posts
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Registered 7 years ago@boo The result is 17.760 if you assume that one half of the people are men and the other half are women.
So 1776 men and 1776 women.
Number of men who get their 45 pounds: 1776/9
Money they receive all men together: (1776/9)*45 = 8880 pounds
Same goes for the women which ends up all in all in (1776/12)*60 = 8880 pounds
Which added up results in 17760 pounds.
After getting this out of the way, look at that divided by 9 and multiplied by 45 in case of men and divided by 12 and multiplied by 60 again. they are the same factor, namely 45/9 or 60/12 which is the factor 5 in both cases.
So no matter how many women or men there are among the people, the average man receives the same amount of money as does the average women which is 5 pounds on average. 3552*5=17760
That being said, is that excercise out of some men/women equlity social engineering book?
Edited by Dangerous_Dan at 11:43:45 08012013 
sport 13,859 posts
Seen 14 hours ago
Registered 12 years ago@boo  if you do the division on each side of the plus sign you're left with:
5x + 17760  5x,
therefore
5x cancels 5x
and you're left with
17760 
Thanks much! 
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