Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Gravitation question

2019 · 10 Jan · Shift 2 · Q66
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Physics
  4. /Gravitation
  5. /2019 · 10 Jan · Shift 2 · Q66

Gravitation question

2019 · 10 Jan · Shift 2 · Q66

JEE MainPhysicsGravitationMCQ+4 / −1
Two stars of masses 3 ×\times× 1031 kg each, and at distance 2 ×\times× 1011 m rotate in a plane about their common centre of mass O. A meteorite passes through O moving perpendicular to the star’s rotation plane. In order to escape from the gravitational field of this double star, the minimum speed that meteorite should have at O is - (Take Gravitational constant; G = 6.67 ×\times× 10–11 Nm2 kg–2)
  1. A
    2.4 ×\times× 104 m/s
  2. B
    1.4 ×\times× 105 m/s
  3. C
    3.8 ×\times× 104 m/s
  4. D
    2.8 ×\times× 105 m/s
View written solutionFree

Correct answer: D

  1. Understand the configuration

Two identical stars each have mass M=3×1031 kgM=3\times 10^{31}\ \text{kg}M=3×1031 kg and the distance between them is 2a=2×1011 m2a=2\times 10^{11}\ \text{m}2a=2×1011 m So each star is at distance a=1011 ma=10^{11}\ \text{m}a=1011 m from the common centre of mass OOO.

The meteorite passes through OOO along a direction perpendicular to the plane of rotation.


  1. Gravitational potential at the centre OOO

Potential due to one star at distance aaa is V1=−GMaV_1=-\frac{GM}{a}V1​=−aGM​ Since there are two identical stars, total potential at OOO is V=−GMa−GMa=−2GMaV=-\frac{GM}{a}-\frac{GM}{a}=-\frac{2GM}{a}V=−aGM​−aGM​=−a2GM​

Substitute values: V=−2(6.67×10−11)(3×1031)1011V=-\frac{2(6.67\times 10^{-11})(3\times 10^{31})}{10^{11}}V=−10112(6.67×10−11)(3×1031)​

V=−2×6.67×3×10−11+31−11V=-2\times 6.67\times 3\times 10^{-11+31-11}V=−2×6.67×3×10−11+31−11

V=−40.02×109=−4.002×1010 J/kgV=-40.02\times 10^9=-4.002\times 10^{10}\ \text{J/kg}V=−40.02×109=−4.002×1010 J/kg


  1. Condition for escape

For minimum escape speed, total mechanical energy at OOO must be zero: 12ve2+V=0\frac{1}{2}v_e^2 + V = 021​ve2​+V=0

So, 12ve2=−V=2GMa\frac{1}{2}v_e^2 = -V = \frac{2GM}{a}21​ve2​=−V=a2GM​

Hence, ve2=4GMav_e^2=\frac{4GM}{a}ve2​=a4GM​

Therefore, ve=4GMa=2GMav_e=\sqrt{\frac{4GM}{a}}=2\sqrt{\frac{GM}{a}}ve​=a4GM​​=2aGM​​


  1. Calculate the value

ve=4(6.67×10−11)(3×1031)1011v_e=\sqrt{\frac{4(6.67\times 10^{-11})(3\times 10^{31})}{10^{11}}}ve​=10114(6.67×10−11)(3×1031)​​

ve=80.04×109v_e=\sqrt{80.04\times 10^9}ve​=80.04×109​

ve=8.004×1010v_e=\sqrt{8.004\times 10^{10}}ve​=8.004×1010​

ve≈2.83×105 m/sv_e\approx 2.83\times 10^5\ \text{m/s}ve​≈2.83×105 m/s


  1. Match with options

ve≈2.8×105 m/sv_e\approx 2.8\times 10^5\ \text{m/s}ve​≈2.8×105 m/s

So the correct option is:

D: 2.8×105 m/s2.8\times 10^5\ \text{m/s}2.8×105 m/s


  1. Comparison with stored correct answer

Stored correct answer: D

My derived answer: D

They agree.

PreviousNext

More from Gravitation

  • A satellite is revolving in a circular orbit at a height h form the earth surface, such that h < < R where R is the earth. Assuming that the effect of earth's atmosphere can be neglected the minimum increase in the speed required so…2019 · MCQ
  • The ratio of the weights of a body on the Earth’s surface to that on the surface of a planets is 9 : 4. The mass of the planet is 91​ th of that of the Earth. If 'R' is the radius of the Earth, what is the radius of the planet ?…2019 · MCQ
  • A satellite of mass M is in a circular orbit of radius R about the centre of the earth. A meteorite of the same mass, falling towards the earth, collides with the satellite completely inelastically. The speeds of the satellite and the…2019 · MCQ
  • A straight rod of length L extends from x = a to x = L + a. The gravitational force it exerts on a point mass 'm' at x = 0, if the mass per unit length of the rod is A + Bx2 , is given by :2019 · MCQ
  • Two satellites, A and B, have masses m and 2m respectively. A is in a circular orbit of radius R, and B is in a circular orbit of radius 2R around the earth. The ratio of their kinetic energies, TA/TB, is ;2019 · MCQ
  • Take the mean distance of the moon and the sun from the earth to be 0.4×106 km and 150×106 km respectively. Their masses are 8×1022 kg and 2×1030 kg respectively. The radius of the earth…2018 · MCQ
  • A body of mass m is moving in a circular orbit of radius R about a planet of mass M. At some instant, it splits into two equal masses. The first mass moves in a circular orbit of radius 2R​, and the other mass, in a circular…2018 · MCQ
  • Suppose that the angular velocity of rotation of earth is increased. Then, as a consequence :2018 · MCQ