A force (F = (b cos⁡θ)/r^3 e _r + (b sin⁡θ)/r^3 e _θ )N is applied on a particle ….

Q: A force $ (F = \frac{b cos⁡θ}{r^3} \hat{e _r} + \frac{b sin⁡θ}{r^3} \hat{e _\theta} $ N is applied on a particle , er is a unit vector along r from origin O of coordinate system and eθ is a unit vector along increasing angle θ . Find the work done by the force F when the particle is taken from point A (a , 0) to B(a , π/2)  on a circular path of radius a.

Numerical

(a) b/a

(b) b/a^2

(c) -b/a^2

(d) -2b/a^2

Ans: (b)