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Applying Newton's 2nd law?

  1. Oct 16, 2009 #1
    Applying Newton's 2nd law?!!!

    1. The problem statement, all variables and given/known data

    A 2.91 kg block starts from rest at the top of a 32◦ incline and slides 1.98 m down the incline in 1.28 s.
    The acceleration of gravity is 9.8 m/s2

    What is the acceleration of the block?
    Answer in units of m/s2

    What is the coefficient of kinetic friction be-
    tween the block and the incline?

    What is the frictional force acting on the
    block?
    Answer in units of N.

    What is the speed of the block after it slid the
    1.98 m? answer in m/s




    2. Relevant equations
    Newtons 2nd's Law

    max=[tex]\sum[/tex]fx=mgsin[tex]\Theta[/tex]

    0=[tex]\sum[/tex] Fy=-mgcos[tex]\Theta[/tex]+n


    3. The attempt at a solution
    I have no idea how to approach this problem.
     
  2. jcsd
  3. Oct 16, 2009 #2

    rock.freak667

    User Avatar
    Homework Helper

    Re: Applying Newton's 2nd law?!!!

    The weight of the block can be split into two components, one parallel to the plane and one perpendicular to the plane.

    What the component parallel to the plane and what is the component perpendicular to the plane?
     
  4. Oct 16, 2009 #3
    Re: Applying Newton's 2nd law?!!!

    The thing to realise is that acceleration is change of velocity over time, and can be related to both velocity and distance.
    I would assume that the acceleration is smooth, and apply the old formula

    s=ut+(1/2)at^2 [s=distance, u=initial velocity, a= acceleration]

    Then I would be able to derive the acceleration that was felt by the block while it slid down the plane, which is a good start.
     
  5. Oct 16, 2009 #4
    Re: Applying Newton's 2nd law?!!!

    using Vx=V cos Theta and Vy=Vsin theta:
    x component= 1.679?
    y component= 1.0492?
     
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