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Gravitation question

2023 · 11 Apr · Shift 2 · Q59
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  5. /2023 · 11 Apr · Shift 2 · Q59

Gravitation question

2023 · 11 Apr · Shift 2 · Q59

JEE MainPhysicsGravitationMCQ+4 / −1
If V\mathrm{V}V is the gravitational potential due to sphere of uniform density on it's surface, then it's value at the center of sphere will be:-
  1. A
    3 V2\frac{3 \mathrm{~V}}{2}23 V​
  2. B
    V2\frac{\mathrm{V}}{2}2V​
  3. C
    43 V\frac{4}{3} \mathrm{~V}34​ V
  4. D
    V\mathrm{V}V
View written solutionFree

Correct answer: A

  1. Potential on the surface of a uniform solid sphere

For a solid sphere of mass MMM and radius RRR, the gravitational potential at the surface is

Vs=−GMRV_s=-\frac{GM}{R}Vs​=−RGM​

The question says this surface potential is VVV. So,

V=−GMRV=-\frac{GM}{R}V=−RGM​

  1. Potential at the center of a uniform solid sphere

For a uniform solid sphere, the gravitational potential at a distance rrr from the center is

V(r)=−GM2R3(3R2−r2)V(r)=-\frac{GM}{2R^3}(3R^2-r^2)V(r)=−2R3GM​(3R2−r2)

At the center, r=0r=0r=0:

Vc=−GM2R3(3R2)=−3GM2RV_c=-\frac{GM}{2R^3}(3R^2)= -\frac{3GM}{2R}Vc​=−2R3GM​(3R2)=−2R3GM​

  1. Relate center potential to surface potential

Since

V=−GMRV=-\frac{GM}{R}V=−RGM​

therefore

Vc=32(−GMR)=3V2V_c=\frac{3}{2}\left(-\frac{GM}{R}\right)=\frac{3V}{2}Vc​=23​(−RGM​)=23V​

  1. Choose the correct option

Thus, the gravitational potential at the center is

3V2\boxed{\frac{3V}{2}}23V​​

So the correct option is A.

Note: Gravitational potential is negative. Hence if surface potential is VVV, center potential is also more negative, and algebraically equal to 3V2\frac{3V}{2}23V​.

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