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Rope attached to wall and car

  1. Aug 13, 2015 #1
    1. The problem statement, all variables and given/known data
    A rope is attached to a wall on one end and to a car on the other end. Someone pushes up on the rope and the car starts to move when the rope makes an angle of 5o with the floor. Mcar=2500kg
    25z3sas.jpg


    2. Relevant equations
    ΣFx=ma
    ΣFy=ma


    3. The attempt at a solution
    Look at the car and the rope separately.

    I'm assuming the car has;
    ΣFx=ma
    ΣFy= 0
    and the rope has the opposite;
    ΣFx= 0
    ΣFy= ma

    But I'm not getting anywhere? Am I doing it right?
     
  2. jcsd
  3. Aug 13, 2015 #2

    sophiecentaur

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    You seems to be mixing up your x and y directions. (And so was i, because I was trying to read the printing laying on its side.:smile:)
    The only force on the car that's accelerating it is horizontal. The trig will tell you what it is at 5o.
    But I don't see how there would be any lower limit to the force needed if there is no friction.
     
  4. Aug 13, 2015 #3

    Doc Al

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    Staff: Mentor

    Nothing is accelerating here. (Not yet, anyway.)

    Start by identifying the forces acting on the truck.
     
  5. Aug 13, 2015 #4

    Doc Al

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    Oops... I didn't notice that it said no friction. (Missed that when trying to read sideways.)

    I don't get the point of the problem. With no friction, you need not be a muscleman to move the truck. A fly could do it.
     
  6. Aug 13, 2015 #5

    sophiecentaur

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    A touch of the "badly written questions' disease, I think.
     
  7. Aug 13, 2015 #6
    So would you need 1N of force up to push to the left?
     
  8. Aug 13, 2015 #7

    sophiecentaur

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    If there's no friction, 1microNewton would produce finite acceleration. The question appears to be flawed - or it's angled to make you spot the nonsense aspect of it.
     
  9. Aug 13, 2015 #8

    Doc Al

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    Indeed. ?:)
     
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