Turn on thread page Beta
    • Thread Starter
    Offline

    7
    ReputationRep:
    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!!
    Offline

    20
    ReputationRep:
    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.
    • Thread Starter
    Offline

    7
    ReputationRep:
    (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. ?
    Offline

    20
    ReputationRep:
    (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 :p:

    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.
    Offline

    0
    ReputationRep:
    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
    Offline

    0
    ReputationRep:
    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!
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: May 17, 2010
Poll
Cats or dogs?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.