Find the work done by the frictional force in drawing a circle of radius r by a pencil of negligible mass with a normal pressing force N ( coefficient of friction `mu_(k)`).

Work done by a frictional force is

Work done by a frictional force is

Work done by a frictional force is

The work done by the frictional force on a surface in a drawing a circle of radius r on the surface by a pencil of negligible mass with a normal pressing force N ( coefficient of friction )is :

Work done by frictional force

Work done by frictional force

Work done by the force of friction

If the normal force is doubled, the coefficient of friction is