Find all forces & the coeff. static friction of a pulley at equilibrium

In summary, the conversation discusses the given masses of two blocks, the force of gravity on each block, and the potential for acceleration and equilibrium. The individual is seeking help with finding friction and tension in the given scenario and is reminded to draw the free body diagrams and consider the relationship between normal force and static friction.
  • #1
minadd
1
0
Homework Statement
It is given that that block a (.5kg) is on a flat surface at rest and block b (.2kg) is hanging over a table attached to a pulley. I tried to find friction but im stuck. And I still have to find tension for block a and b. I've had experience will inclines but forgot how to do flat surfaces...
Relevant Equations
Fg = mg
g= 9.81ms^2
(Sigma)F = ma
Ff = (mu)Fn
Given:
(block a) m = .500kg
(block b) m = .200kg
that's all...
Fg (block a) = (.5)(9.81) = 4.905N = Fn
Fg (block b) = (.2)(9.81) = 1.962N

i think acceleration might go like...
a = (1.962)/(.5 + .2) = 2.8m/s^2 but isn't it supposed to be at equilibrium? So 0m/s^2.
How am I supposed to find friction without acceleration?

the photo attached is the question.
 

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  • #2
minadd said:
Homework Statement: It is given that that block a (.5kg) is on a flat surface at rest and block b (.2kg) is hanging over a table attached to a pulley. I tried to find friction but I am stuck. And I still have to find tension for block a and b. I've had experience will inclines but forgot how to do flat surfaces...
Homework Equations: Fg = mg
g= 9.81ms^2
(Sigma)F = ma
Ff = (mu)Fn

Given:
(block a) m = .500kg
(block b) m = .200kg
thats all...
Fg (block a) = (.5)(9.81) = 4.905N = Fn
Fg (block b) = (.2)(9.81) = 1.962N

i think acceleration might go like...
a = (1.962)/(.5 + .2) = 2.8m/s^2 but isn't it supposed to be at equilibrium? So 0m/s^2.
How am I supposed to find friction without acceleration?

the photo attached is the question.
You are trying to jump to the end without doing the work of setting up the problem. The first task to draw the FBDs, the same as every other mechanics problem. Once you have all of the forces on each mass drawn and labeled, you can write the force balance equation for each mass and solve the equations.
One thing that might help: static friction is a force that holds an object still by preventing it from sliding along a surface. It is directly proportional to the normal force of the surface on the object.
 
  • #3
tnich said:
static friction is a force that holds an object still by preventing it from sliding along a surface. It is directly proportional to the normal force of the surface on the object.
Small correction: the maximum static friction force is directly proportional to the normal force of the surface on the object. The actual force is whatever force, up to that limit, that is required to prevent sliding.
 
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Likes tnich

1. What is the coefficient of static friction?

The coefficient of static friction is a dimensionless quantity that represents the amount of force needed to overcome the static friction between two surfaces in contact. It is denoted by the symbol μ and can range from 0 to 1.

2. How is the coefficient of static friction determined?

The coefficient of static friction can be determined experimentally by measuring the maximum force needed to overcome the static friction between two surfaces in contact and dividing it by the normal force between them.

3. What is the difference between static and kinetic friction?

Static friction is the force that prevents two stationary surfaces from sliding against each other, while kinetic friction is the force that opposes the motion of two surfaces that are already in motion.

4. How do you calculate the forces acting on a pulley at equilibrium?

To calculate the forces acting on a pulley at equilibrium, you need to consider all the forces acting on the pulley, including the weight of the pulley and any external forces, and use the principle of equilibrium which states that the sum of all forces acting on an object must be equal to zero.

5. How does the coefficient of static friction affect the motion of a pulley?

The coefficient of static friction determines the maximum amount of force that can be applied to the pulley before it starts to move. If the applied force is less than the maximum static friction, the pulley will remain at rest. If the applied force exceeds the maximum static friction, the pulley will start to move.

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