Because the block is not moving, the sum of the y components of the forces acting on the block must be zero. Find an expression for the sum of the y components of the forces acting on the block, using coordinate system b. Express your answer in terms of some or all of the variables Fn , Ff , Fw , and θ . View Available Hint(s)for Part C ∑Fy=0

Fncos(θ)+Ffsin(θ)−Fw

Previous Answers Correct Part D Part complete Because the block is not moving, the sum of the x components of the forces acting on the block must be zero. Find an expression for the sum of the x components of the forces acting on the block, using coordinate system b. Express your answer in terms of some or all of the variables Fn , Ff , Fw , and θ . View Available Hint(s)for Part D ∑Fx=0

−Fnsin(θ)+Ffcos(θ)

Previous Answers Correct Part E To find the magnitude of the normal force, you must express Fn in terms of Fw since Ff is an unknown. Using the equations you found in the two previous parts, find an expression for Fn involving Fw and θ but not Ff . View Available Hint(s)for Part E Hint 1for Part E. How to approach the problem From your answers to the previous two parts you should have two force equations ( ∑Fy=0 and ∑Fx=0 ). Combine these equations to eliminate Ff . The key is to multiply the equation for the y components by cosθ and the equation for the x components by sinθ , then add or subtract the two equations to eliminate the term Ffcos(θ)sin(θ) . An alternative motivation for the algebra is to eliminate the trig functions in front of Fn by using the trig identity sin2(θ)+cos2(θ)=1 . At the very least this would result in an equation that is simple to solve for Fn .

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