Can you do this?
missmarple
Posts: 1,980
I'm having a brainfart this morning so bare with me:
If an aircraft is flying at 3000ft and wants to descend to 2000ft at a rate of 350ft per minute, how many minutes will this take?
Obviously it will be 2 minutes something.....
But how would you go about working it out?
If an aircraft is flying at 3000ft and wants to descend to 2000ft at a rate of 350ft per minute, how many minutes will this take?
Obviously it will be 2 minutes something.....
But how would you go about working it out?
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Comments
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(350/60) x 300 = ?
Oops- other way round- (60/350) x 300I'd give my right hand to be ambi-dextrous0 -
350 divide 60 = 5.833333333 = ft per second
300 divide 5.8333333333 = 51.42857
So takes 2mins 51.42857 secs
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Hmm is that correct? For time = distance/speed....?
So 350ft / 60 = 5.83 per second....
300ft / 5.83 = 51 seconds + 2 mins.....
Everyone else get the same answer sans calculator?0 -
I'd demand SI units first.
Feet and minutes indeed...0 -
total decent = 1000ft
1000/350 = 2.8 minutes
0.8 of a minute = 0.8x60seconds = 48 seconds
so it's 2min 48 seconds....i think....Santa Cruz Chameleon
Orange Alpine 1600 -
MacAndCheese wrote:total decent = 1000ft
1000/350 = 2.8 minutes
0.8 of a minute = 0.8x60seconds = 48 seconds
so it's 2min 48 seconds....i think....
This.
I don't know where the 350/60 and 300's are coming from.0 -
bails87 wrote:MacAndCheese wrote:total decent = 1000ft
1000/350 = 2.8 minutes
0.8 of a minute = 0.8x60seconds = 48 seconds
so it's 2min 48 seconds....i think....
This.
I don't know where the 350/60 and 300's are coming from.
This is the other one I came up with; looks to be a bit more orderly!
Cheers for that. 8)0 -
MacAndCheese wrote:total decent = 1000ft
1000/350 = 2.8 minutes
0.8 of a minute = 0.8x60seconds = 48 seconds
so it's 2min 48 seconds....i think....
1000/350 is not 2.8: it is 2.857.
Enter that and you get the same as the 1st poster ;-)
The answer to the nearest second is 171 seconds, or 2 mins 51s.0 -
3000ft starting.
after 1 minute you will have descended 350ft so will be at 2650ft
after 2 minutes you will have descended 700ft (350 + 350) so will now be at 2300ft.
You therefore have a further 300 ft to descend down to your target of 2000ft.
in 60 seconds (1 minute) you will drop another 350ft which is too far.
350/60 will give you your descent per second rate = 5.83 ft per second.
You need to drop 300ft so 300/5.83 will give you the number of seconds required to drop 300ft.
= 51.5 seconds.
Plus your 2 minutes!
Alternatively, we know that you drop 5.83 feet per second, and the total drop is 1000ft
1000/5.83 = 171.5 seconds which is 2mins 51.5 seconds.0 -
Surely both are semi-correct? As SS pointed out. I've got this assessment on Tuesday which involves numeracy, 25 questions in 12 minutes so calculator not allowed nor a viable option.
My potential answers are 48, 51 and 52. Taking decimals into account. And this is a multiple choice test - sod's law they'll have those 3 and another obscure one like 3 minutes.
I'd go with 48 seconds.
For example, if you travel 84 miles in 14 minutes, what is your MPH?
60/14 = 4.3 roughly therefore 4.3 * 84 = 361. 2 roughly, again without calculator.
Everyone in agreement?0 -
48 seconds is not even within a second of the absolute answer, which is as in the first post is 2mins 51.42857 (to 5 decimal places).
Round that to the nearest second and it is 2 mins 51 seconds.
You have to decide how accurate you want to be, and how to round it.0 -
2 min 51.4 seconds - you can do it in your head!
1000ft to descend, 350ft/min
Take the 0s off to make things easier = 100ft, 35ft/min
You want to do 100/35. 35 goes in to 100 twice (35*2 = 70) with a remainder (30), so there is your two minutes.
Now you 've got to do 30/35 to see how long the remainder takes. 30/35 = 6/7. 1/7 is approx 0.143, multiplied by 6 = 0.857.
The remainder is still in minutes, mind, so multiply by 60 to get it into seconds = 0.857*60 = 51.4.
Time taken = 2 minutes 51.4 seconds.0 -
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supersonic wrote:MacAndCheese wrote:total decent = 1000ft
1000/350 = 2.8 minutes
0.8 of a minute = 0.8x60seconds = 48 seconds
so it's 2min 48 seconds....i think....
1000/350 is not 2.8: it is 2.857.
Enter that and you get the same as the 1st poster ;-)
The answer to the nearest second is 171 seconds, or 2 mins 51s.
He said sans calculator....thats the best I could do in my head!Santa Cruz Chameleon
Orange Alpine 1600 -
So if going at 270fpm the answer would not be 3 mins and 42 seconds?
But:
27/6 = 4.5
So: 190/4.5 = 42 seconds
Therefore 3 mins and 42 seconds.0 -
270 fpm:
1000/270 = 3.703 minutes.
0.703 of a minute is 60x0.703 seconds = 42.18 seconds.
So 3 mins 42 secs rounded.
So yep, you are correct! Often more than one way of doing it, the key is to be careful with decimal places. Use lots when calculating, then round at the end.0 -
Ahh proper bo! Now I can do jack shit for the rest of the day knowing full well that I have fulfilled my maths problem.
Thank you for all your help chaps!
What about if it took 3 mins 42 seconds to descend 1000ft; what was your fpm?
3 mins 42 = 600/162 = 3.7
1000/3.7 = 270fpm
Sorted! 0 -
Depends ... If the wings where to suddenly fall off whilst said plane was descending, it would fall a lot quicker :twisted:0
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It's a trick question, I wouldn't be on the aeroplane in the first place.
Sorry0 -
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Is it a laden aircraft or unladen?0
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You're not an air traffic controller are you?0
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Good luck for tommorow.......
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