Could you me with this question?
one iron block of 70 n it is at rest on a slope of 40 degrees, what is the magnitude of the static friction force that is directed up the plane? is it necessarily the maximum static friction force? what is the normal force with this angle?

Magnitude of static friction force is 70 sin40° = 44.99 N.  

No, it is not necessary that it is maximum static friction.

Normal force is equal to 70 cos40° = 53.62 N.

Explanation:

We apply newton law of moton equation along the plane and perpendicular to plane;

Along the plane,

70 sin 40° =  ---------------(1)

70 cos 40° = N --------------(2)

= μN -----------------(3)

So, it depends on the value of μ that the friction is maximum or not .

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