A large spool of copper wire is placed on a 30.0 degree incline plane. The loose

Question

A large spool of copper wire is placed on a 30.0 degree incline plane. The loose end of the wire comes off of the top edge of the spool and is attached to a rigid pole at the top of the incline. The spool is not moving.

a) Is there a normal force on the spool? If so, at what point does it act on the spool?

b) What minimum coeffiecent of static friction will keep th spool from sliding down the incline?

c) If the mass of the spool id 100 kg, what is the smalles wire thickness that will keep the wire from snapping?

Explanation / Answer

It is mentioned that the upper end of spool is loose , means no tenstion at upper it .thus th component of weight of spool must be balanced by friction force .

A. Presence of friction clearly tells that normal force should be non zero .

B. Also to balnce other component of weight there should be nonzero normal force

Thus

a) normal force will be present = mg cos30°

And it will act throughout the wire , at every point

b )minimum friction must be mgsin30°Thus minimum coefficient = tan30° = 0.577

I am not getting part C .

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