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Homework Help: Easy problem dealing with tension and mass of an object.

  1. Dec 8, 2011 #1
    1. The problem statement, all variables and given/known data
    The box on the frictionless ramp is held at rest by the tension force. The mass of the box is 20kg. What is the value of the tension force?

    2. Relevant equations
    sine=opp/hyp cosine=adj/hyp F=ma

    3. The attempt at a solution
    Did 20*9.8 to get the force of gravity on the object (196N). Then I took the cosine of 30 and got .866. I then divided 196 by this and got 226N for the hypotenuse. Is this correct? Thanks!
    DIAGRAM:http://img838.imageshack.us/img838/6927/diagramu.png [Broken]

    EDIT: So, the newtons needed to hold it when the slope is 0 would be 196. I also found the newtons for it at 89 degrees, which was about 11,000. So, according to my math, the tension force is 226N. Now I just need to find the normal force. Any ideas?
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Dec 8, 2011 #2


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    Homework Helper

    Re: Easy problem dealing with tension and mass of an object. REALLY EASY!

    Each of those calculations is correct, but now you have to relate them to the question.

    EDIT: if the angle of the slope was 0o what value would you get from your calculations, and what tension would be needed to keep the mass in place?
    Last edited by a moderator: May 5, 2017
  4. Dec 8, 2011 #3
    Mmmm... I did the same problem and got 98 N for tension. Remember that the direction of normal force is perpendicular to surface, and it isn't antiparallel to the force of gravity. You have to find the components of the force of gravity, too.
    Add all components and set it equal to zero, since it is at rest.
  5. Dec 8, 2011 #4
    The normal force is equal to a component of the force of gravity. (Try to find out which one:))
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