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Homework Help: Problem about a wheel

  1. Nov 18, 2014 #1
    1. The problem statement, all variables and given/known data
    So for a project, we decided to do tension strings that would be attached to a wheelchair inside a subway so that when the subway decelerates or accelerates, the wheelchair wouldn't move.
    However, due to our inexperience we used only the wheel and solved for equations.
    If I'm not mistaken when the subway is deccelerating, the force (ma) is applied to the left, the friction force would also be to the left (since it's movement would keep going right due to inertia) and the Tension would go to the right, even if the tension cables are attached to the left.
    Something like it was attached
    So what we wanted to find was what was the Tension force necessary so that the wheel wouldnt move.
    uk = 0.20
    radius = 0.3048m
    mass = 89.67
    acceleration = +- 1.5m/s^2
    Since I can't seem to attach any file
    Tension ->
    Normal would be going up ^
    mg would be going down v
    and Force + friction force would be going to the left <-
    2. Relevant equations
    Sum of forces in x: T - F - f = 0
    Sum of forces in y:N - mg = 0
    Torque force = r x F
    Sum of torques??

    3. The attempt at a solution
    Normal force = 878.766
    Friction force = 175.752
    Applied force = 134.505
    Torque force = 0.3048 * 175.752 * sin 90 = 53.5692

    The problem is that I am not sure at all on how to use the torque force or if im supposed to use this in a sum of torques equation etc.
  2. jcsd
  3. Nov 23, 2014 #2
    Thanks for the post! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Nov 23, 2014 #3


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    Gold Member

    So the wheelchair is facing along the carriage (or the opposite direction), not across?
    Where and how are the strings attached? Horizontally at the tops of the wheels?
    I don't know what you are saying there.
    You first need to say which way the decelerating carriage is moving, in your mental image. Sounds like it's to the right.
    What force is applied 'to the left', other than friction and the tension? Is this a fictional 'inertial' force in the frame of reference of the decelerating carriage?
    Where exactly is this friction?
    Tension goes both ways, so whether it's to the left or to the right depends on which of the two objects it's attached to is under consideration.
    How about describing the set up in more detail, assigning labels to points (e.g. O for centre of wheel etc.)?
    Depending on the set-up, torque could lead to the wheelchair toppling, so it may be important.
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