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M1 Kinematics 2nd rather interesting question

http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/January%202011%20-%20QP/6677_01_que_20110119.pdf
Q2- It's similar to the last ''rather interesting kinematics question'' I posted however you have to solve for u. I cannot :tongue:

You can easily do it using v=u+at however it shouldn't work since this uses the wrong pos/neg sign for acceleration (and it's the 3 mark part)
I've tried so much but to no avail- please help!
I'm feeling doubtful about success on M1/2 :/ Any tips/ advice? I've done the whole kinematics chapter and shouldn't find this hard.

(edited 9 years ago)

Reply 1

TenOfThem

Original post by MathMeister

You can easily do it using v=u+at however it shouldn't work since this uses the wrong pos/neg sign for acceleration (and it's the 3 mark part)

v=u+at

up = +ve

-6.45 = u - 9.8*0.75

u = 7.35 - 6.45 = 0.9

No issue with +/- being wrong

What did your working look like?

Reply 2

AltairAlAstorah

That's exactly the same working as mine, can't see where the original poster went wrong tbh

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Reply 3

TeeEm

Original post by MathMeister

Original post by TenOfThem

v=u+at

up = +ve

-6.45 = u - 9.8*0.75

u = 7.35 - 6.45 = 0.9

No issue with +/- being wrong

What did your working look like?

I think the issue is misunderstanding on how to correctly use the notion of displacement inn this type of question

Reply 4

TenOfThem

Original post by TeeEm

I think the issue is misunderstanding on how to correctly use the notion of displacement inn this type of question

We did not use displacement

I think the issue is that the OP does not understand the suvat quantities or equations and he does not realise that direction matters

Reply 5

TeeEm

Original post by TenOfThem

We did not use displacement

I think the issue is that the OP does not understand the suvat quantities or equations and he does not realise that direction matters

inaccurate language in my part ...

I mean the notion of direction in these quantities, when the direction of motion changes and the motion is considered as a whole.

Reply 6

AltairAlAstorah

Agreed, to the OP, the signs used are negative because of the direction of the acceleration and final velocity (down). The original velocity is positive due to it's direction (up)

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Reply 7

TenOfThem

Original post by TeeEm

inaccurate language in my part ...

I mean the notion of direction in these quantities, when the direction of motion changes and the motion is considered as a whole.

I thought you might mean that :smile:

Reply 8

MathMeister

Original post by TenOfThem

We did not use displacement
I think the issue is that the OP does not understand the suvat quantities or equations and he does not realise that direction matters

No no no no no no no no . The ''OP'' does understand lol- it's just that I forgot it. Everybody makes careless mistakes sometimes. Yeah- I didn't use -6.45 I used 6.45- oops.

(edited 9 years ago)

Reply 9

TenOfThem

Original post by AltairAlAstorah

We could have used down as positive and got u=-0.9

Then said it was 0.9 as it was up

Reply 10

TenOfThem

Original post by MathMeister

No no no no no no no no . The ''OP'' does understand lol- it's just that I went full ... when doing it. Everybody makes careless mistakes sometimes. Yeah- I didn't use -6.45 I used 6.45- oops.

Which demonstrates a lack of understanding

If it is not understanding of the actual direction then it is carelessness - which suggests a lack of understanding regarding the importance of direction

(edited 9 years ago)

Reply 11

MathMeister

Original post by TenOfThem

Which demonstrates a lack of understanding

If it is not understanding of the actual direction then it is carelessness - which suggests a lack of understanding regarding the importance of direction

I know it's importance. I wasn't thinking. It's carelessness and tiredness.

Reply 12

TenOfThem

Original post by MathMeister

I know it's importance. I wasn't thinking. It's carelessness and tiredness.

ok

go to bed now

Reply 13

Super199

Original post by MathMeister

I know it's importance. I wasn't thinking. It's carelessness and tiredness.

That's what they all say :tongue:

Reply 14

MathMeister

Original post by TenOfThem

ok
go to bed now

No you? I can do what I darn well want to do on a weekend. I could just retract the last statement and put it down to carelessness. In fact I'm not even tired.

Reply 15

MathMeister

Original post by TenOfThem

ok
go to bed now

Hypocrite?- Do you even remember what you pm'd me for?

Reply 16

TenOfThem

Original post by MathMeister

No you? I can do what I darn well want to do on a weekend. I could just retract the last statement and put it down to carelessness. In fact I'm not even tired.