edexcel maths, units in mechanics Watch

Iconic_panda
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do we need to include units in mechanics? if i decide to include units should i leave them in the bracket to avoid confusion?
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NR22
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Just don’t put units is the safer option, units are never required in the exam and an examiner should ignore them but you never know whether a harsh examiner would mark it wrong if they felt that because you got the units wrong it shows a lack of understanding. Just don’t put them. Always remember to put every answer to 3s.f. you will lose the last accuracy if you are over accurate, and this is still the same if you get; a surd in core maths you would leave it as a surd since it’s exact but in mechanics you should write the surd down then write an extra line with the surd wrote to 3s.f.; if you get an integer like 7548N then you need to still write it to 3s.f. So 7550N people tend to lose the last accuracy mark on ones like this the most because they go “well that’s a nice integer answer” so leave it... just no! Always write to 3s.f and don’t put units.
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Prasiortle
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(Original post by Iconic_panda)
do we need to include units in mechanics? if i decide to include units should i leave them in the bracket to avoid confusion?
(Original post by NR22)
Just don’t put units is the safer option, units are never required in the exam and an examiner should ignore them but you never know whether a harsh examiner would mark it wrong if they felt that because you got the units wrong it shows a lack of understanding. Just don’t put them. Always remember to put every answer to 3s.f. you will lose the last accuracy if you are over accurate, and this is still the same if you get; a surd in core maths you would leave it as a surd since it’s exact but in mechanics you should write the surd down then write an extra line with the surd wrote to 3s.f.; if you get an integer like 7548N then you need to still write it to 3s.f. So 7550N people tend to lose the last accuracy mark on ones like this the most because they go “well that’s a nice integer answer” so leave it... just no! Always write to 3s.f and don’t put units.
Post #2 is completely wrong. Units can be required in the mark scheme, and if you understand the content, you should be able to figure out what the correct unit for your answer is. There should not be any "confusion" as this is really quite basic.
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NR22
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(Original post by Prasiortle)
Post #2 is completely wrong. Units can be required in the mark scheme, and if you understand the content, you should be able to figure out what the correct unit for your answer is. There should not be any "confusion" as this is really quite basic.
Hi so before you start saying I’m wrong, are you an examiner? because I’ve also asked a senior examiner about this before and they have said not to put units for M1. I will say to the person who original asked the question you can feel free to listen to who you want but if you put units that’s fine just don’t get them wrong but you are only adding a stress to your own situation as they are not needed.
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Iconic_panda
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Are units really that serious I thought the mark scheme says they don't care about units anyways
I mean what i plan to do is not write units in the first line, e.g u=5, then I will probably say at the end, so the speed after collision is 5ms-1
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MCArth
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(Original post by NR22)
Hi so before you start saying I’m wrong, are you an examiner? because I’ve also asked a senior examiner about this before and they have said not to put units for M1. I will say to the person who original asked the question you can feel free to listen to who you want but if you put units that’s fine just don’t get them wrong but you are only adding a stress to your own situation as they are not needed.
Might depend on exam board? Pretty sure I've seen a mark scheme that wanted units - but nonetheless units are extremely easy. The only ones you need really for M1 are ms^-1 ms^-2 N Nm, and there's not much else. M1 is pretty darn straightforward.
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Iconic_panda
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sorry to ask what exam board is this from?
(Original post by MCArth)
Might depend on exam board? Pretty sure I've seen a mark scheme that wanted units - but nonetheless units are extremely easy. The only ones you need really for M1 are ms^-1 ms^-2 N Nm, and there's not much else. M1 is pretty darn straightforward.
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MCArth
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(Original post by Iconic_panda)
sorry to ask what exam board is this from?
Edexcel - but I'm assuming you're on a different exam board since Edexcel's M1 has already been sat
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NR22
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(Original post by MCArth)
Might depend on exam board? Pretty sure I've seen a mark scheme that wanted units - but nonetheless units are extremely easy. The only ones you need really for M1 are ms^-1 ms^-2 N Nm, and there's not much else. M1 is pretty darn straightforward.
I would say they are very easy and straightforward if you understand mechanics but if someone is asking do I need to put units because I’m not fully confident with mechanics then I do know from tutoring that some students would get so confused with them because they don’t understand what the units are saying, but edexcel are not bothered about units in M1
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Iconic_panda
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Yeah nah I'm looking at M2
(Original post by MCArth)
Edexcel - but I'm assuming you're on a different exam board since Edexcel's M1 has already been sat
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Iconic_panda
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the situation is that if the question asks to find out the value of u, i assume you don't need a unit for that because its just a value. if they ask you to find out the speed after collision for instance, then i feel like its essential to include unit but should I include the unit on the same line as my answer or the line after my answer?
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MCArth
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(Original post by Iconic_panda)
Yeah nah I'm looking at M2
Well I would give units to be safe most of the time. From the start of an edexcel mark scheme "Omission of units or incorrect units is not (usually) counted as an accuracy error." - keyword usually, so if I were you I would be on the safe side. Units are very hard to get wrong and if it's a question where the units don't matter getting them wrong won't matter.
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MCArth
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(Original post by Iconic_panda)
the situation is that if the question asks to find out the value of u, i assume you don't need a unit for that because its just a value. if they ask you to find out the speed after collision for instance, then i feel like its essential to include unit but should I include the unit on the same line as my answer or the line after my answer?
I usually just write the answer, then the units, then (3sf).
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Prasiortle
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(Original post by Iconic_panda)
sorry to ask what exam board is this from?
(Original post by NR22)
Hi so before you start saying I’m wrong, are you an examiner? because I’ve also asked a senior examiner about this before and they have said not to put units for M1. I will say to the person who original asked the question you can feel free to listen to who you want but if you put units that’s fine just don’t get them wrong but you are only adding a stress to your own situation as they are not needed.
E.g. Edexcel says "Omission of units or incorrect units is not usually counted as an accuracy error", meaning that sometimes it could be counted as an accuracy error leading to loss of a mark.

Also try telling anyone who e.g. works at NASA that "units are not needed" - they lost over $125 million when the Mars Climate Orbiter was lost in 1999 because various teams weren't clear about whether they were using metric or imperial units. Similarly in 1983 an Air Canada aircraft almost crashed because a unit conversion error meant that it took off with only half the required quantity of fuel.
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Iconic_panda
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also if they don't give unit in the question then i shouldnt create one right? just checking
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_gcx
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I don't see why you wouldn't include units if they're given...
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NR22
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(Original post by Prasiortle)
E.g. Edexcel says "Omission of units or incorrect units is not usually counted as an accuracy error", meaning that sometimes it could be counted as an accuracy error leading to loss of a mark.

Also try telling anyone who e.g. works at NASA that "units are not needed" - they lost over $125 million when the Mars Climate Orbiter was lost in 1999 because various teams weren't clear about whether they were using metric or imperial units. Similarly in 1983 an Air Canada aircraft almost crashed because a unit conversion error meant that it took off with only half the required quantity of fuel.
Not sure if you have realised but he/she doesn’t work for NASA and is sitting his/her Alevel’s and therefore things are best kept as simple as possible because it’s when you over complicate things that you lose marks at Alevel. And thank you for clearing that you are not an examiner and therefore had no right in saying that I was incorrect before. Please know to only give advice when you are sure in your answer and don’t discredit people’s answers who have more understanding of mark schemes than you.
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Prasiortle
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(Original post by Iconic_panda)
also if they don't give unit in the question then i shouldnt create one right?
In mechanics units will usually be given in the question, but if they're not (e.g. with centre of mass/lamina problems where it doesn't matter what unit the mass is in), then yes, just leave the answer without units.
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Iconic_panda
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yeah I was thinking in collision they usually just say something is moving at the speed of u so in that case we don't need any units right?
(Original post by Prasiortle)
In mechanics units will usually be given in the question, but if they're not (e.g. with centre of mass/lamina problems where it doesn't matter what unit the mass is in), then yes, just leave the answer without units.
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Prasiortle
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(Original post by NR22)
Not sure if you have realised but he/she doesn’t work for NASA and is sitting his/her Alevel’s and therefore things are best kept as simple as possible because it’s when you over complicate things that you lose marks at Alevel. And thank you for clearing that you are not an examiner and therefore had no right in saying that I was incorrect before. Please know to only give advice when you are sure in your answer and don’t discredit people’s answers who have more understanding of mark schemes than you.
Do you not understand what usually means? It means you could lose a mark for not giving the correct units, as the user MCArth has pointed out a few posts ago as well. Also "you're overcomplicating it" is the usual excuse given by idiots who want to think that something is difficult when it's really not. If you have any actual understanding, rather than just being a robot who blindly substitute numbers into formulae, then units will be entirely trivial.
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