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Gravitation question

2024 · 5 Apr · Shift 1 · Q67
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  5. /2024 · 5 Apr · Shift 1 · Q67

Gravitation question

2024 · 5 Apr · Shift 1 · Q67

JEE MainPhysicsGravitationMCQ+4 / −1

Match List I with List II :

LIST I LIST II
A. Kinetic energy of planet I.
−GMm/a-\mathrm{GMm} / \mathrm{a}−GMm/a
B. Gravitation Potential energy of sun-planet system II.
GMm/2a\mathrm{GMm} / 2 \mathrm{a}GMm/2a
C. Total mechanical energy of planet III.
Gmr\frac{\mathrm{Gm}}{\mathrm{r}}rGm​
D. Escape energy at the surface of planet for unit mass object IV.
−GMm/2a-\mathrm{GMm} / 2 \mathrm{a}−GMm/2a

(Where a=\mathrm{a}=a= radius of planet orbit, r=\mathrm{r}=r= radius of planet, M=\mathrm{M}=M= mass of Sun, m=\mathrm{m}=m= mass of planet)

Choose the correct answer from the options given below :

  1. A
    (A)-(II), (B)-(I), (C)-(IV), (D)-(III)
  2. B
    (A)-(I), (B)-(II), (C)-(III), (D)-(IV)
  3. C
    (A)-(III), (B)-(IV), (C)-(I), (D)-(II)
  4. D
    (A)-(I), (B)-(IV), (C)-(II), (D)-(III)
View written solutionFree

Correct answer: A

  1. Use standard results for a planet in circular orbit of radius aaa around the Sun

For a planet of mass mmm orbiting a Sun of mass MMM:

  • Gravitational potential energy: U=−GMmaU=-\frac{GMm}{a}U=−aGMm​
  • From centripetal force, mv2a=GMma2⇒v2=GMa\frac{mv^2}{a}=\frac{GMm}{a^2}\Rightarrow v^2=\frac{GM}{a}amv2​=a2GMm​⇒v2=aGM​
  • Hence kinetic energy: K=12mv2=12m⋅GMa=GMm2aK=\frac12 mv^2=\frac12 m\cdot \frac{GM}{a}=\frac{GMm}{2a}K=21​mv2=21​m⋅aGM​=2aGMm​
  • Total mechanical energy: E=K+U=GMm2a−GMma=−GMm2aE=K+U=\frac{GMm}{2a}-\frac{GMm}{a}=-\frac{GMm}{2a}E=K+U=2aGMm​−aGMm​=−2aGMm​
  1. Escape energy at the surface of the planet for unit mass object

Escape energy for unit mass from a planet of mass mmm and radius rrr is the minimum energy needed to make total energy zero:

Eescape=GmrE_{\text{escape}}=\frac{Gm}{r}Eescape​=rGm​

  1. Now match List I with List II
  • A. Kinetic energy of planet K=GMm2aK=\frac{GMm}{2a}K=2aGMm​ So, A →\to→ II

  • B. Gravitational potential energy of sun-planet system U=−GMmaU=-\frac{GMm}{a}U=−aGMm​ So, B →\to→ I

  • C. Total mechanical energy of planet E=−GMm2aE=-\frac{GMm}{2a}E=−2aGMm​ So, C →\to→ IV

  • D. Escape energy at the surface of planet for unit mass object Eescape=GmrE_{\text{escape}}=\frac{Gm}{r}Eescape​=rGm​ So, D →\to→ III

  1. Final matching

A→II,B→I,C→IV,D→IIIA\to II,\quad B\to I,\quad C\to IV,\quad D\to IIIA→II,B→I,C→IV,D→III

This corresponds to Option A.

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