UK-Cherub Forum
Off Topic => Banter => Topic started by: Phil Alderson on January 20, 2009, 06:57:14 PM
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I am trying to study for an exam and one question has me stumped, I should be able to work it out but can't.
Two objects leave a point at the same time, one travelling at 10 m/s and the other at 23m/s an observer sees the first one and then three hours later sees the second. How far away is the origin point?
This should be easy to work out but I just can't get it.
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First it is best to get all the units straightened out, so 3 hours = 60 x 60 x 3 = 10800 Seconds
Let the car going 10m/s be A and the one at 23m/s be B
As car A arrives at the point 3 hours after B we know it is 108000m behind (10800 seconds x 10m/s)
Lets let X equal the distance car A has already travelled so at the time t when car B passes the observer we can say they have travelled...
for A, X metres and B X + 108000 metres
Distance = Speed x Time so Time = Distance/Speed
So Car A t = X/10
and Car B t = (X + 108000)/23
As the time for both to reach these respective points is the same we can put both equations equal to eachother so
X/10 = (X + 108000)/23
so
2.3X = X + 108000
1.3X = 108000
X = 83076... metres
Add this to the distance Car B is ahead (108000) and the origin is therefore 191076m (rounded a little)
To check we can see how long it would take each car to cover this distance, for Car A 191076/10 = 19107.6 or 5.3 Hours
And B 191076/23 = 8307... or 2.3 Hours
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Thanks Tom, A it makes sence now and B the answer we were supplied is wrong.
Phil
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Here is a silly little maths thing, It kept me entertained!
Three men each have ten pounds and decide they want to buy a cow. They each give their ten pounds to a fourth man, the middle man, who goes off to buy a cow. The middle man buys a cow for 25 pounds and decides to keep 2 pounds as commission for his services. He then distributes the remaining three pounds among the three investors, leaving them with 1 pound change each.
Each of the three men has therefore spent 9 pounds and the middle man has kept 2 pounds. 3 X 9 is 27 + 2 = 29 where is the last pound?
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There is no extra pound. The cow cost £25 + £2 Commission = £27.
But pedigree livestock is (or was until very recently: I haven't checked) sold in guineas (1 guinea = 21 shillings = £1.05p) and there will also normally be some luck money from the vendor to the buyer, so livestock purchase is much more complicated than you might think!
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JimC you are right pedigree cattle are still sold in guineas and you would usually get luck money but generally only at auction