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Homework Help: Newton's Second Law

  1. Oct 9, 2014 #1
    Renee is on Spring Break and pulling her 21-kg suitcase through the airport at a constant speed of 0.47
    m/s. She pulls on the strap with 120 N of force at an angle of 38° above the horizontal.

    What is the normal force and the total resistance force (friction and air resistance) experienced by the suitcase?

    I do not understand how to find the forces since it is constant speed and not acceleration. I also don't know how the angle is relative to this question.
  2. jcsd
  3. Oct 9, 2014 #2
    Have you tried drawing a free body diagram? Using a free body diagram is a very important part of correctly solving physics problems. From the free body diagram, what are the forces acting on the suitcase? Write a force balance in the horizontal and vertical directions. Why do you feel that, unless there is acceleration, you cannot write a force balance?

  4. Oct 10, 2014 #3


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    What Chet said.

    Newtons second law (mentioned in the title of your post) normally relates to situations where the forces are unbalanced (eg situations involving acceleration). In this case the problem statement talks about constant speed so no acceleration. What do you know about forces when there is no acceleration?
  5. Oct 10, 2014 #4


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    Two words for you: vector components.
  6. Oct 10, 2014 #5
    3 words: Free Body Diagram
  7. Oct 10, 2014 #6


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    Four words: draw the damn diagram !
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