Easy physics questions, please check my answers

  1. 1. The problem statement, all variables and given/known data
    When you sit on a chair, the resultant force on you is ..?
    3. The attempt at a solution
    Down, because of gravity?

    1. The problem statement, all variables and given/known data
    In the absence of an external force, a moving object will:
    stop immediately
    slow down and eventually come to a stop MY ANSWER
    go faster and faster
    move with constant velocity

    1. The problem statement, all variables and given/known data
    An object is placed on an inclined plane. The angle of the incline is gradually increased until the object begins to slide. The angle at which this occurs is theta. What is the coefficient of static friction between the object and the plane?
    2. Relevant equations
    tan(theta)
    That's what I understood, but I need to make sure...

    Thanks!
     
  2. jcsd
  3. All of your answers are incorrect. Try again, draw force diagrams and really think these problems through.
     
  4. For the first one, the force on the chair is down, but the force on me is up... Would this be correct?
     
  5. For the second one, I reviewed the laws, and I would say that the velocity would stay constant (unless some external force came into play). Would this be correct?
     
  6. berkeman

    Staff: Mentor

    Yes, that's better. For the second question, start with F=ma.


    EDIT -- And I believe that your answer for the 3rd one is correct, [tex]\mu_s = tan( \Theta )[/tex]
     
    Last edited: Feb 27, 2007
  7. Are you absolutely sure my last answer is incorrect?...

    The Prenhall website has the same question. I entered an answer other than tan to make sure, and I got:
    An object is placed on an inclined plane. The angle of incline is gradually increased until the object begins to slide. The angle at which this occurs is θ. What is the coefficient of static friction between the object and the plane?

    Your Answer:
    sin θ

    Correct Answer:
    tan θ
     
  8. You mean that if F doesn't change, and m doesn't change, a will be constant?
     
  9. berkeman

    Staff: Mentor

    That is correct.
     
  10. berkeman

    Staff: Mentor

    No, I mean that if there is no external force, the acceleration is zero. And you correctly inferred that this means the velocity is constant.
     
  11. Thank you!
     
  12. the resultant force on me is mg upward where m is my mass angd is acceleration due to gravity
     
  13. in absence of external force body moves with constant velocity
     
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