What is the maximum frictional force?

• Shaye
In summary, the conversation is about calculating the maximum frictional force of a block on a 35 degree angle incline. The speaker initially calculates the force to be 69N, while the book states it to be 675N. However, it is pointed out that the book has made an error by confusing weight with mass in their calculations. The correct answer is 69N, and the book is identified as "Advance Physics for You." The conversation ends with relief that the speaker's calculations were correct.
Shaye
Homework Statement
The block in the diagram weighs 120N. It will start to slip down the slope when the component of it's weight acting down the slop equals the maximum frictional force. If the block slips when the angle Θ = 35 degrees what is the maximum frictional force?
Relevant Equations
Sin(Θ)*Opposite = Hypotenuse and F=Ma
In the attachment I am supposed to calculate the maximum frictional force of a block on a 35 degree angle incline (that is the point at which the force acting opposite frictional force is highest)

I make it out to be sin(35)*120N = 69N but the book says 675N and it gives it as cost(55)*120N*9.81. But given F=Ma how so?

I don't understand this or something has slipped my mind. The diagonal force component (hypotenuse) should be 69N because the veridical component is 120N.

Thanks

Attachments

• 20201107_163943.jpg
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The book has confused weight with mass in producing their answer. They've erroneously multiplied the weight in Newtons by 9.81, or g. One multiplies a mass by g to get force due to gravity. But they've provided that force already as a weight of 120 N.

Shaye and TSny
What book is this? I am thinking of creating a Physics Forum page of book corrections.

gneill said:
The book has confused weight with mass in producing their answer. They've erroneously multiplied the weight in Newtons by 9.81, or g. One multiplies a mass by g to get force due to gravity. But they've provided that force already as a weight of 120 N.

Phew! Thanks. I thought I was going mad

1. What is frictional force?

Frictional force is a type of force that opposes the motion of an object when it comes into contact with another surface.

2. How is frictional force measured?

Frictional force is measured in units of Newtons (N) using a force meter or spring scale.

3. What factors affect the maximum frictional force?

The maximum frictional force is affected by the type of surfaces in contact, the force pushing the surfaces together, and the roughness of the surfaces.

4. How does the maximum frictional force affect the motion of an object?

The maximum frictional force can either slow down or prevent the motion of an object, depending on the direction and magnitude of the applied force.

5. Can the maximum frictional force ever be exceeded?

No, the maximum frictional force is a limit and cannot be exceeded. However, the amount of frictional force can be reduced by using lubricants or by changing the surface materials.

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