# M2: ladder resistance to friction

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all forces are in perfect equilibrium because it's on the verge of slipping.

Therefore, the forces: friction is acting towards the wall, and the ladders mass is acting in the centre?

how do I work out the horizontal force of the ladder and the particle?

Therefore, the forces: friction is acting towards the wall, and the ladders mass is acting in the centre?

how do I work out the horizontal force of the ladder and the particle?

Last edited by Maths&physics; 1 year ago

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#3

Resolve vertically to find the normal reaction at A (noting that there cannot be any vertical components of forces at B). Then use F = (mu)R at A.

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(Original post by

Resolve vertically to find the normal reaction at A (noting that there cannot be any vertical components of forces at B). Then use F = (mu)R at A.

**old_engineer**)Resolve vertically to find the normal reaction at A (noting that there cannot be any vertical components of forces at B). Then use F = (mu)R at A.

because friction is acting in the opposite direction and is parrallel to R2, is friction: mu(R2)?

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#5

(Original post by

theres a reaction force from the ladder at the ground (R1) and a reaction force agasint the wall (R2).

because friction is acting in the opposite direction and is parrallel to R2, is friction: mu(R2)?

**Maths&physics**)theres a reaction force from the ladder at the ground (R1) and a reaction force agasint the wall (R2).

because friction is acting in the opposite direction and is parrallel to R2, is friction: mu(R2)?

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No. F = (mu)R1. Find F first. Then R2 must be equal and opposite to F (as they are the only horizontal forces and the net horizontal force must be zero).

**old_engineer**)No. F = (mu)R1. Find F first. Then R2 must be equal and opposite to F (as they are the only horizontal forces and the net horizontal force must be zero).

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#7

(Original post by

ok, but why do we use R1 for friction, when ffriction is acting in a perpendicular direction?

**Maths&physics**)ok, but why do we use R1 for friction, when ffriction is acting in a perpendicular direction?

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That’s always the case when an object is on the point of slipping. F is the friction and R is the normal reaction at the same point.

**old_engineer**)That’s always the case when an object is on the point of slipping. F is the friction and R is the normal reaction at the same point.

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#9

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for part b and working out moments about A, do i take the reaction for the centre of the ladder and the reactioon force (reece) at point c?

**Maths&physics**)for part b and working out moments about A, do i take the reaction for the centre of the ladder and the reactioon force (reece) at point c?

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(Original post by

There’s nothing in the question to say that the ladder is not uniform, so I think we can assume it is uniform, in which case it’s weight acts vertically downwards from its mid-point. The reaction at C acts horizontally in the direction away from the wall.

**old_engineer**)There’s nothing in the question to say that the ladder is not uniform, so I think we can assume it is uniform, in which case it’s weight acts vertically downwards from its mid-point. The reaction at C acts horizontally in the direction away from the wall.

also, i don't understand what they're asking in c.

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#11

(Original post by

so, do we ignore it's reaction in taking moments?

also, i don't understand what they're asking in c.

**Maths&physics**)so, do we ignore it's reaction in taking moments?

also, i don't understand what they're asking in c.

Part c is probably looking for you say that treating the person as a particle allows you to identify accurately where the weight of the person is acting.

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#12

(Original post by

x

**Maths&physics**)x

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(Original post by

Why do you make a separate post for your attachments out of interest? You’re not the only one who does this and I’ve always wondered why.

**Notnek**)Why do you make a separate post for your attachments out of interest? You’re not the only one who does this and I’ve always wondered why.

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(Original post by

If taking moments about A you can ignore the forces acting at A ( because the distance is zero) but you must include any force acting at C, including the horizontal reaction of the wall on the ladder.

Part c is probably looking for you say that treating the person as a particle allows you to identify accurately where the weight of the person is acting.

**old_engineer**)If taking moments about A you can ignore the forces acting at A ( because the distance is zero) but you must include any force acting at C, including the horizontal reaction of the wall on the ladder.

Part c is probably looking for you say that treating the person as a particle allows you to identify accurately where the weight of the person is acting.

is the horizontal reaction of the wall a summation of the horizontal reaction of the ladder and the person?

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#15

(Original post by

thank you.

is the horizontal reaction of the wall a summation of the horizontal reaction of the ladder and the person?

**Maths&physics**)thank you.

is the horizontal reaction of the wall a summation of the horizontal reaction of the ladder and the person?

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(Original post by

That terminology is not correct. If taking moments about A it would be correct to say that the sum of the clockwise moments of the ladder and the person must equal the anticlockwise moment of the normal reaction at B.

**old_engineer**)That terminology is not correct. If taking moments about A it would be correct to say that the sum of the clockwise moments of the ladder and the person must equal the anticlockwise moment of the normal reaction at B.

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#17

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ok, im confused. what happens to the reaction force of the person standing on the ladder, why are we ignoring it? if a car is on a slope, we have a reaation force of that person on the ladder.

**Maths&physics**)ok, im confused. what happens to the reaction force of the person standing on the ladder, why are we ignoring it? if a car is on a slope, we have a reaation force of that person on the ladder.

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(Original post by

If you were trying to determine whether or not the person would slip down the ladder, you would have to find the normal reaction of the ladder to the person’s weight. However that is not what has been asked for in this question.

**old_engineer**)If you were trying to determine whether or not the person would slip down the ladder, you would have to find the normal reaction of the ladder to the person’s weight. However that is not what has been asked for in this question.

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