- #1

UnknownGuy

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## Homework Statement

A block of mass 20kg is on rest on a rough plane inclined at 60 degrees to the horizontal. A force P is applied to the block to "maintain equilibrium". P is parallel to the line of greatest slope of the inclined plane. The maximum value of P is twice the minimum value of P. Find the coefficient of friction between the block and the plane.

## Homework Equations

Frictional force=Coefficient of friction*Normal Foce (F=μR)

## The Attempt at a Solution

This question can be interpreted in two different ways:

First way: Without P, the block will slide down so P

**MUST**act up the line of greatest slope of the plane.

Second way: P can either act up or down the line of greatest slope of the plane, and the resultant of P, component of the weight down the slope and the frictional force is 0N.

Attached are pictures illustrating the two methods. Can you please tell me which method do you think is correct? In my exam, I was leaning towards the second way but μ=5.20 seemed rather large. Moreover, the wording, "To maintain equilibrium" made it seem like the block would be sliding down without P hence it has to act up the line of greatest slope.

Thanks in advance.

Edit: It seems like the quality of the pictures has been decreased. The subscripts under P are (min) and (max)