Weight of block and static friction

[rcmango]

Homework Statement

The weight of the block in the drawing is 84.0 N. The coefficient of static friction between the block and the vertical wall is 0.520.


(a) What minimum force is required to prevent the block from sliding down the wall? in Newtons

(b) What minimum force is required to start the block moving up the wall? (Hint: The static frictional force is now directed down the wall.)
in Newtons

Homework Equations

The Attempt at a Solution

having problems figuring this out, is there a formula for the force sliding down the wall.
also, wouldn't the minimum be the .520 just the static force?

thanks.

 

[Astronuc]

For a static situation, the friction (using static coefficient) must equal the weight.

Friction is given by the product of normal force and coefficient of friction $\mu$.


To get the block moving vertically, the applied force must exceed the weight AND friction.


Friction acts in either (both) directions.