Dismiss Notice
Check out the new Application Assistant, where you can calculate your LizzyM score, see how you rank compared to other applicants, and see a list of schools where similar students were accepted.

EK 1001 physics #277

Discussion in 'MCAT Study Question Q&A' started by divinelyawesome, 05.19.14.

  1. SDN is made possible through member donations, sponsorships, and our volunteers. Learn about SDN's nonprofit mission.
  1. divinelyawesome

    divinelyawesome

    Joined:
    04.03.14
    Messages:
    9
    Status:
    Medical Student (Accepted)
    I'm geting confuse about the application of newton second law here:

    The plane above is inclined at a 60 degrees angle. The coefficient of static friction is 0.2. The mass is 100 kg. What is the minimum force F necessary to start the object moving up the plane? Basically, the object is being pulled up the incline by a cord. So we have:
    Sum of forces in x direction=T-f-W.sin(60degrees)=m.a
    In y direction:N=W.cos(60)
    a is zero in y direction, but I don't understand why it's zero in the x direction. If the object is moving upward, it has an acceleration. Should I assume it's moving at cst velocity?
     
  2. SDN Members don't see this ad. About the ads.
  3. syoung

    syoung MS-3 5+ Year Member

    Joined:
    01.02.11
    Messages:
    1,032
    Location:
    Over the rainbow
    MDApps:
    Status:
    Medical Student
    If it's moving it doesn't mean it has acceleration. You need to look at all of your forces.
     
  4. DrknoSDN

    DrknoSDN

    Joined:
    02.21.14
    Messages:
    450
    Status:
    Pre-Medical
    In this question it would be accelerating but that isn't relevant. They gave you coefficient of static friction and at a certain force you will overcome that static friction and have less friction because the coefficient of kinetic friction is smaller.
    That's why the question asked at what minimum force will it break free of the kinetic friction and begin to move.

    Basically once it starts sliding it will continue sliding.
    This is true for just about every scenario with friction because kinetic is always smaller than static.
     
  5. divinelyawesome

    divinelyawesome

    Joined:
    04.03.14
    Messages:
    9
    Status:
    Medical Student (Accepted)
    Okay, I get it. Thanks guys.
     

About the ads

Share This Page