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.

 

[ogb p]

I can provide a response to your question. The formula for calculating the minimum force required to prevent the block from sliding down the wall is given by:
F = μs * W
where F is the minimum force required, μs is the coefficient of static friction, and W is the weight of the block. Substituting the given values, we get:
F = 0.520 * 84.0 N = 43.68 N
Therefore, a minimum force of 43.68 N is required to prevent the block from sliding down the wall.

For the second part of the question, the minimum force required to start the block moving up the wall is the same as the static frictional force acting downwards. This can be calculated using the same formula as before, but with a different direction for the force:
F = μs * W
F = 0.520 * 84.0 N = 43.68 N
Therefore, a minimum force of 43.68 N is required to start the block moving up the wall.

I hope this helps to clarify your understanding of the problem. Remember, the coefficient of static friction is a measure of the maximum frictional force that can be exerted between two surfaces in contact before they start sliding against each other. In this case, the minimum force required is equal to the static frictional force.