Coefficient of friction depends upon

equal to

The force required to move the body up the plane will be minimum if it makes an angle with the inclined plane equal to the angle of friction.

upward at its upper end

A ladder is resting on a smooth ground and leaning against a rough vertical wall. The force of friction will act upward at its upper end.

zero at its upper end

A ladder is resting on a rough ground and leaning against a smooth vertical wall. The force of friction will act zero at its upper end.

less than

In a screw jack, the effort required to lower the load is less than the effort required to raise the same load.