# A Level Maths Mechanics question

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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??

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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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.

Can someone honestly just explain the whole question to me cause mechanics is gonna be the death of me fr.

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#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

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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(Original post by

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

**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

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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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.
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#6

**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

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#7

(Original post by

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.

**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.

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#8

(Original post by

i worked it all out, got the first answer right but cannot do question b

**nitron10**)i worked it all out, got the first answer right but cannot do question b

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#9

**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.

+ 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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(Original post by

Where can I find the answers? I worked it out but I cant seem to find the answers online

**lara147**)Where can I find the answers? I worked it out but I cant seem to find the answers online

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#12

(Original post by

It’s ocr alevel maths pure & mechanics 2018 paper. The mark scheme is on the ocr website

**ccchimpo**)It’s ocr alevel maths pure & mechanics 2018 paper. The mark scheme is on the ocr website

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(Original post by

Oh okay thanks I got both answers right do you still want to see the working out I did?

**lara147**)Oh okay thanks I got both answers right do you still want to see the working out I did?

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