# A Level Maths Mechanics question

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Thread starter 1 month ago
#1
Can someone help with this question.

Says A is on the point of moving down the plane and is on a rough plane.
So shouldn't horizontal motion be greater than tension and friction? So the equation of motion be:
mgsin30 - F - T = ma ?? (where F is friction and mgsin30 is resolving parallel to the plane)
The mark scheme's equations:
T + F - mgsin30 = ma (for part (a)(ii))
T - F - mgsin30 = ma (for part (b))
But that would mean tension > horizontal motion, meaning A is moving up the plane??
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Thread starter 1 month ago
#2
Here's the question with diagram:

Can someone honestly just explain the whole question to me cause mechanics is gonna be the death of me fr.
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1 month ago
#3
Have you drawn the force diagram and labelled everything?

The system is on the point of moving (limiting equilibrium) so the forces pulling up and the forces pulling down exactly equal each other

In part aii and part b, the value of lambda and mu are different, that’s why you get different equations
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Thread starter 1 month ago
#4
(Original post by laurawatt)
Have you drawn the force diagram and labelled everything?

The system is on the point of moving (limiting equilibrium) so the forces pulling up and the forces pulling down exactly equal each other

In part aii and part b, the value of lambda and mu are different, that’s why you get different equations
Ohh ok so for part (a) forces up equal forces down.
For part (b) though, because it is now accelerating, I thought the equation for particle A would be mgsin30 - T - F = 1/4 mg , but the mark scheme says T - F - mgsin30 = 1/4 mg.
Particle A is moving down the slope so shouldn't horizontal force be greater than tension + friction ?
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Thread starter 1 month ago
#5
Oh wait nvm. My error was linking part (a) to part (b), when they are independent of each other. If lambda is 2 then the mass of B is greater than that of A so rather than A moving down the slope, it is now moving up the slope.
1
1 month ago
#6
(Original post by laurawatt)
Have you drawn the force diagram and labelled everything?

The system is on the point of moving (limiting equilibrium) so the forces pulling up and the forces pulling down exactly equal each other

In part aii and part b, the value of lambda and mu are different, that’s why you get different equations
i worked it all out, got the first answer right but cannot do question b
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1 month ago
#7
(Original post by ccchimpo)
Here's the question with diagram:

Can someone honestly just explain the whole question to me cause mechanics is gonna be the death of me fr.
Do you know what the answers are?
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1 month ago
#8
(Original post by nitron10)
i worked it all out, got the first answer right but cannot do question b
Where can I find the answers? I worked it out but I cant seem to find the answers online
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1 month ago
#9
(Original post by ccchimpo)
Here's the question with diagram:

Can someone honestly just explain the whole question to me cause mechanics is gonna be the death of me fr.
That’s definitely MEI! Did you go and see the additional assessments 2021, I believe they have the same type of questions on this.
+ this doesn’t look like a 2020 mechanics (I’ve done this paper before in my school) I’m thinking it’s a 2019 P1
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Thread starter 1 month ago
#10
(Original post by lara147)
Where can I find the answers? I worked it out but I cant seem to find the answers online
It’s ocr alevel maths pure & mechanics 2018 paper. The mark scheme is on the ocr website
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Thread starter 1 month ago
#11
Mark Scheme:
https://www.ocr.org.uk/Images/535623...-mechanics.pdf

It is Q12
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1 month ago
#12
(Original post by ccchimpo)
It’s ocr alevel maths pure & mechanics 2018 paper. The mark scheme is on the ocr website
Oh okay thanks I got both answers right do you still want to see the working out I did?
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Thread starter 1 month ago
#13
(Original post by lara147)
Oh okay thanks I got both answers right do you still want to see the working out I did?
Yes please, that’d be awesome!
1
1 month ago
#14
(Original post by ccchimpo)
Yes please, that’d be awesome!
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Thread starter 1 month ago
#15
(Original post by lara147)
Thank you so much that helped so much!
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