What is the key step to solving this cylinder friction problem?

[drewdiddy]

Homework Statement

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Homework Equations

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The Attempt at a Solution

I understand everything about the problem except how to determine the angle P makes with the new horizontal axis (parallel with F)--see diagram under primary one... so that I can sum the forces up and answer the problem. My geometry is somewhat rusty and I'm not exactly sure what geometric property makes the angle 45. Any help is appreciated.

 

[RTW69]

Your solution looks correct to me. You summed the moments at B to get P=812 nt. You resolved the Ff and N into components in the x and y direction (all the angles look to be 45 degrees). You summed the forces in the in the x and y direction =0 and solved for mu.

 

[kleyb08]

HELP me on this problem please it involves a cylinder and i can't figure out the correct solution.
(see attachment)

Here is the question:

Determine magnitude of force P that will cause the cylinder rotates.

Weight of Cylinder = 400N
Radius of Cylinder = 150mm
Coefficient of friction in all surfaces is = 0.2

 

[RTW69]

I would draw a free body diagram of the cylinder. There will be normal and frictional forces on the A and B surfaces. Resolve P into X & Y directions. One of the things you will need to convince yourself of, by geometry, is if a line segment drawn from the origin (where A & B meet) through the center of the circle and connecting to P is a 90 degree angle. If it does you can take the moment about the origin and get rid of some of the ugliness relating to the frictional forces. Summing forces in the X & Y directions plus the moment equation should give you enough equations to solve the problem.

 

[kleyb08]

I would draw a free body diagram of the cylinder. There will be normal and frictional forces on the A and B surfaces. Resolve P into X & Y directions. One of the things you will need to convince yourself of, by geometry, is if a line segment drawn from the origin (where A & B meet) through the center of the circle and connecting to P is a 90 degree angle. If it does you can take the moment about the origin and get rid of some of the ugliness relating to the frictional forces. Summing forces in the X & Y directions plus the moment equation should give you enough equations to solve the problem.

can you please help me setup the equation or can u illustrate the proper solution for this problem i really don't know how to start with please help i need solution thanks,

 

[RTW69]

Have you done a free body diagram of the cylinder, that is the first step? Choose a coordinate system such as the directions of sides A and B. Resolve the P force in the direction of the coordinate system you have chosen. P is the hypotenuse of a 3-4-5 triangle so you know all the angles associated with P. Sum the forces in the x, y direction and take the moment about the origin. You will end up with 3 three equations and 3 unknowns one of which is P. You can use your knowledge of linear equations to solve for the three unknowns.