1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Normal Force Problem

  1. Nov 25, 2013 #1
    1. The problem statement, all variables and given/known data

    Find Normal Contact force between the sphere and wedge A and wall B.
    All surfaces are frictionless and in rest.
    Diagram :-

    2. The attempt at a solution

    Let normal force on A be N and on B be R.
    My Diagram :-

    By The Diagram,
    N = mgcosθ ....eq(1)
    R = Nsinθ ...eq(2)
    = mgcosθsinθ

    But the answer if :- N = (mg)/cosθ
    it is not matching with eq(1).
    How is this possible?
    Please help me out and explain why it is wrong

    Attached Files:

  2. jcsd
  3. Nov 25, 2013 #2
    N is not equal to mgcosθ. There is a component of R along N. Draw a separate FBD for the sphere showing the three forces.
  4. Nov 25, 2013 #3
    But how N is not equal to mgcosθ and is R = Nsinθ correct component
  5. Nov 25, 2013 #4
    R=Nsinθ is correct. As I said before, there is a component of R along N so you will have to take that into account while balancing the forces in the direction normal to wedge. Do you see now?
  6. Nov 25, 2013 #5
    But how N is not equal to mgcosθ?
  7. Nov 25, 2013 #6


    User Avatar
    Homework Helper

    R also has a component parallel to N.

    Resolve N into horizontal and vertical components. The sum of all forces is zero, and that is valid to the horizontal and vertical components, separately.

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted