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## Homework Statement

**A block of mass**

Now, assume that the value of θ is

*m*is at rest on an inclined plane of angle θ with respect to the horizontal. There is friction between the block and the inclined surface (μk and μs).Now, assume that the value of θ is

**the value in part A) (so that the block will remain stationary if no other forces act on it). What is the maximum magnitude of a horizontal Force F that(with respect to ground) can be applied without causing the block to move up the incline?***less than*## Homework Equations

## The Attempt at a Solution

**I have found a similar thread here:**

https://www.physicsforums.com/threads/block-wedge-problem.698343/#post-4424430

and here: https://www.physicsforums.com/threads/box-on-an-incline-with-friction-min-and-max-forces-involved.619902/

I understand everything except one significant detail. I have to choose between several options:

mg(sinθ−μ*cosθ)/(cosθ+μ*sinθ)

https://www.physicsforums.com/threads/block-wedge-problem.698343/#post-4424430

and here: https://www.physicsforums.com/threads/box-on-an-incline-with-friction-min-and-max-forces-involved.619902/

I understand everything except one significant detail. I have to choose between several options:

mg(sinθ−μ*cosθ)/(cosθ+μ*sinθ)

**or mg(sinθ+μ*cosθ)/(cosθ+μ*sinθ)**

**Friction is static. I don't understand the numerator. Why is there -/+**

**μ*sinθ or****-/+****μ*cosθ?? Could you give me a hint?**