An Object of Mass,m,is Placed in an Arc of a Circle

Multiple Choice

An object of mass,m,is placed in an arc of a circle of radius,r.The coefficient of kinetic friction between the object and the surface of the arc is $\mu$ _k.What is the work done by friction in going from P₁ and P₂?

A) - $\mu$ _kmg r (cos( $\theta$ ₂) -cos( $\theta$ ₁) )
B) - $\mu$ _kmg r (sin( $\theta$ ₂) -sin( $\theta$ ₁) )
C) - $\mu$ _kmg r cos( $\theta$ ₂) sin $\theta$ ₁)
D) - $\mu$ _kmg r sin( $\theta$ ₂) cos( $\theta$ ₁)
E) none of the above