JEE Advanced · Physics · 6. Work Power Energy

The work done on a particle of mass m by a force $K [\frac{x}{{(x^{2} + y^{2})}^{3 / 2}} \hat{i} + \frac{y}{{(x^{2} + y^{2})}^{3 / 2}} \hat{j}]$ (K being a constant of appropriate dimensions, when the particle is taken from the point (a,0) to the point (0,a) along a circular path of radius a about the origin in the x-y plane is

A $\frac{2 K π}{a}$
B $\frac{K π}{a}$
C $\frac{K π}{2 a}$
D 0

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Answer & Solution

Correct Answer

(D) 0

Step-by-step Solution

Detailed explanation

$d w==\vec{F} \cdot d \vec{r}=\vec{F} \cdot(d x \hat{i}+d y \hat{j})=K \int$ $\frac{x d x}{\left(x^2+y^2\right)^{3 / 2}}+\frac{y d y}{\left(x^2+y^2\right)^{3 / 2}}$
$x^2+y^2=a^2$
$w =\frac{ K }{ a ^3} \int_{ a }^0 xdx +\int_0^{ a } ydy =\frac{ K }{ a ^3}\left(\frac{- a ^2}{2}+\frac{ a ^2}{2}\right)=0$.

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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The work done on a particle of mass m by a force K x x 2 + y 2 3 / 2 i ^ + y x 2 + y 2 3 / 2 j ^ (K being a constant of appropriate dimensions, when the particle is taken from the point (a,0) to the point (0,a) along a circular path of radius a about the origin in the x-y plane is

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