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koikeeper
25 Mar 20 11:57
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Date Joined: 02 Aug 07
| Topic/replies: 25,534 | Blogger: koikeeper's blog
A question my son was given.

An electric train accelerates uniformly from rest, to reach 55km /p/h in 6mins.
Determine the total time taken to travel 10km.
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Report howard March 25, 2020 11:07 AM GMT
If you can work out how far it's travelled in 6 mins it should be easy. I can't !
Report Darlo Bantam March 25, 2020 11:08 AM GMT
6 minutes 45 seconds. (I think).
Report Johnny_Mustang March 25, 2020 11:10 AM GMT
If it's on the Jubilee Line, about three f**king hours.
Report GLASGOWCALLING March 25, 2020 11:15 AM GMT
Wheres Mart when you need him . ?? Cry
Report Ramruma March 25, 2020 11:16 AM GMT
Are you sure OP's son read the question right? Six minutes to accelerate to 55 kph seems absurdly slow.
Report Willie Shafter. March 25, 2020 11:20 AM GMT
his sons only 7
Report ItsMeSwaddle March 25, 2020 11:21 AM GMT

Mar 25, 2020 -- 12:16PM, Ramruma wrote:


Are you sure OP's son read the question right? Six minutes to accelerate to 55 kph seems absurdly slow.


Not when a few members of this forum are on board.

Report the dealer March 25, 2020 11:27 AM GMT
I will guess 6mins 58 seconds
Report koikeeper March 25, 2020 11:35 AM GMT
Howard, neither can I lol
Report Willie Shafter. March 25, 2020 11:37 AM GMT
as ram says...approx 2 min to get to 11mph..another 2 mins to reach 23mph..another 2 mins to reach 34mph..

maybe thats irrelevant and its only for the purpose of the calculation.
Report the dealer March 25, 2020 11:37 AM GMT
I was thinking, probably miles out but if you work it out per second 55 divided by 360, gives you 0.152 km per second.
Report the dealer March 25, 2020 11:40 AM GMT
then again I got a D for Maths O'Grade  Laugh
Report rooster booster March 25, 2020 11:40 AM GMT
Is the answer "FISH" ?
Report koikeeper March 25, 2020 11:41 AM GMT
I got 0 level maths, far too long ago now though...even the grandsons homework is hard lol
Report TheNorfolkMafia March 25, 2020 11:43 AM GMT
https://www.youtube.com/watch?v=s71atR_VHPs

A little something like what I wrote earlier!

Wink
Report uwgs March 25, 2020 11:47 AM GMT
For the first 6 minutes the train averaged 55/2 km/ph, (the average between 0 km/ph and 55 km/ph) and so would have travelled 2.75 kms in the 6 minutes. That leaves 7.25 kms to go at 55 km/ph which would take approx another 7.9 minutes. So the 10km journey will have taken 6 minutes plus 7.9 minutes making a total of 13.9 minutes.
Report Darlo Bantam March 25, 2020 11:50 AM GMT
Yeah, that's right. I forgot to divide the first half by 2 so had it travelling twice as far as it was meant to do in the first six minutes.
Report G Hall March 25, 2020 11:51 AM GMT
Exactly
Report the dealer March 25, 2020 12:00 PM GMT
Aye leave it to the experts, all makes sense now SadGrin
Report irishone March 25, 2020 12:01 PM GMT
Need more information here ?

What sort of snow is on the line please ?
Report koikeeper March 25, 2020 12:11 PM GMT
Cheers uwgs.
Report koikeeper March 25, 2020 12:12 PM GMT
Dealer, you sound like me lol
Report stewarts rise March 25, 2020 12:19 PM GMT
Is that correct? The train reached 55km/p/h accelerating uniformly, aren't you assuming that it will travel at 55km/p/h for the rest of the journey?
Can't recall velocity from donkeys years ago but i assumed the train would continue to accelerate.
Report madhatters March 25, 2020 12:22 PM GMT
Just a slight dent in uwg methodology
If the average was 55kph then it must have travelled faster at some point
The question doesnt quote the average though
GL Grin
Report madhatters March 25, 2020 12:23 PM GMT
Surprised you don't know the answer Koi
Being red hot at point to point Laugh
Report posy March 25, 2020 12:26 PM GMT
average wasn't 55.....max was.....uwg is correct
Report Willie Shafter. March 25, 2020 12:26 PM GMT
he said averaged 55/2 which is 27.5 kmph
Report GLASGOWCALLING March 25, 2020 1:15 PM GMT
Report pablo-fanque March 25, 2020 1:26 PM GMT
just out of interest , where was the train going ?
Report 1stpost March 25, 2020 1:52 PM GMT
It takes 6 min to reach 55km/hr and covers 2.75km......leaving 7.25 km to go @55km/hr.
i.e. 7.91 mins...total time 13.91 mins..
Report 1stpost March 25, 2020 2:01 PM GMT
Think of it like this...the end velocity is 55km/hr,....or approx 1 km /min.
So, to cover the whole 10 @1km/ min would take 10 mins...but its first got to reach the end speed which takes 6 min.
This takes up 2.75 km...leaving 7.25 @approx 1 km/min...
Report madhatters March 25, 2020 2:11 PM GMT
Maths is not in question
Assumption of top speed is
Call Stewart R for the defence
Old proverb once told  - Assume makes an ass of u and me

Was it an essential journey btw
& did they have any egg & cress sandwiches available

Stick to me times tables Grin
Report six_six_six March 25, 2020 2:32 PM GMT
11 minutes 26.49secs to 2dp

work in metres and seconds using

v = u + at
and
s=ut+at^2/2

starts from rest so u = 0

we know v (55kph at time t 6 minutes, hence derive a)
want t at s= 10k so plug in derived a and derive t
Report rooster booster March 25, 2020 2:34 PM GMT
What's the voltage and how big is tthe flux capacitor
Report breadnbutter March 25, 2020 2:50 PM GMT
9.166666666666 mins  would be the answer I think they are looking for but it's prob completey wrong, not had a look at the replies yet,the lack of info in the question is typical of school **** now.
Report breadnbutter March 25, 2020 2:51 PM GMT
What age group is this for?
Report breadnbutter March 25, 2020 2:53 PM GMT
Oops
Cell 1 Cell 2
Cell 3 Cell 4
Report TheNorfolkMafia March 25, 2020 3:16 PM GMT
Report breadnbutter March 25, 2020 3:27 PM GMT
It only asks how long to travel 10km, not how long to travel the first 10km of a journey.Its a trick question imo.
Report Darlo Bantam March 25, 2020 3:54 PM GMT
v = u + at
and
s=ut+at^2/2


Well, those equations take me back. Probably A-level maths classes
Report thegiggilo March 25, 2020 4:03 PM GMT
s=1/2(u+v)t to find the distance traveled in first six minutes. Then 10-ans to give the rest of the distance inthe journey. This can then be divided by 55 multiplied by 60 to give the time for the rest of the journey. Add firstsix to this to give thetotal length of time.
Report 1stpost March 25, 2020 4:03 PM GMT
^^,no,  when i was at school 50s/early 60s this was o level maths
Report thegiggilo March 25, 2020 4:05 PM GMT
s=1/2(u+v)t to find the distance traveled in first six minutes. Then 10-ans to give the rest of the distance inthe journey. This can then be divided by 55 multiplied by 60 to give the time for the rest of the journey. Add firstsix to this to give thetotal length of time

13.9..
Report Darlo Bantam March 25, 2020 4:22 PM GMT

Mar 25, 2020 -- 5:03PM, 1stpost wrote:


^^,no,  when i was at school 50s/early 60s this was o level maths


>When schools say exams aren't getting easier, ignore them (to a point definitely). For our a-level practice, we did previous year's o-level papers as that's how much the maths syllabus had changed.

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