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# M1 question - dynamics watch

1. Hi,

I am having a real problem knowing where to start with this question:

A body of mass 2kg is held in limiting equilibrium on a rough plane inclined at 20 degrees to the horizontal by a horizontal force X. the coefficient between the body and the plane is .2. modelling the body as a particle find X when the body is on the point of slipping

a) up the plane b) down the plane

Thank you!!
2. Draw a force diagram
Resolve all the forces parallel/perpendicular to the plane
The particle is stationary, so the net force must be zero

Note that if the particle is on the point of slipping up the plane, friction will point down the plane, and vice versa.
3. (Original post by tazarooni89)
Draw a force diagram
Resolve all the forces parallel/perpendicular to the plane
The particle is stationary, so the net force must be zero

Note that if the particle is on the point of slipping up the plane, friction will point down the plane, and vice versa.
hi, thank you i'm just not sure how to do the normal things you would do with so little values such as we are not given x etc. ?
4. (Original post by monkeyytastic)
hi, thank you i'm just not sure how to do the normal things you would do with so little values such as we are not given x etc. ?
Of course you're not given X, that's what you're trying to find

You know the value of gravity, the mass of the particle, the slope of the plane, and the coefficient of friction.

From the mass and gravity, you can calculate the weight
From the weight and angle, you can calculate normal reaction
From the normal reaction and coefficient of friction, you can calculate the friction

You've found three forces above. Those forces, plus X, must all be balanced, so resolve them parallel and perpendicular to the plane, and make sure everything cancels out - which allows you to work out X.
5. If you give me your email address I will send you a drawing showing a little trick you can do to make your life easier with the force diagrams
6. On page 88 example 15 there's an easy to understand explanation of the question you're talking about in your edexcel M1 book.

Resolve perpendicular to the slope:
R=2gcos20+Xsin20

Resolve to slope:
F+2gsin20=Xcos20

as it's in limiting equilibrium and you're given that μ is 0.2
you sub 0.2R into the equation you got ''F+2gsin20=Xcos20" for F to get:

.2(2gcos20) +.2Xsin20+2gsin20=Xcos20

=

10.388=Xcos20-.2Xsin20
10.388=0.871X
X=11.92

That is for a) up the slope and it's the answer in the back of the book. I got stuck on this question and just posting this solution for anyone else that gets stuck. Remember it's given a method on page 88 example 15 of your edexcel M1 workbooks.

Hope this helped even if it was a little late!

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