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

2016 · 10 Apr · Shift 1 · Q58
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. /2016 · 10 Apr · Shift 1 · Q58

Gravitation question

2016 · 10 Apr · Shift 1 · Q58

JEE MainPhysicsGravitationMultiple correct+4 / −1
An astronaut of mass m is working on a satellite orbiting the earth at a distance h from the earth’s surface. The radius of the earth is R, while its mass is M. The gravitational pull FG on the astronaut is :
  1. A
    Zero since astronaut feels weightless
  2. B
    0 < FG < GMmR2{{GMm} \over {{R^2}}}R2GMm​
  3. C
    GMm(R+h)2{{GMm} \over {{{\left( {R + h} \right)}^2}}}(R+h)2GMm​< FG <GMmR2{{GMm} \over {{R^2}}}R2GMm​
  4. D
    FG = GMm(R+h)2{{GMm} \over {{{\left( {R + h} \right)}^2}}}(R+h)2GMm​
View written solutionFree

Correct answer: B, D

  1. Gravitational force at distance R+hR+hR+h from Earth's center

The astronaut is at height hhh above the Earth's surface, so his distance from the center of the Earth is

r=R+h.r=R+h.r=R+h.

By Newton's law of gravitation, the gravitational pull on the astronaut is

FG=GMm(R+h)2.F_G=\frac{GMm}{(R+h)^2}.FG​=(R+h)2GMm​.

  1. Check whether it is zero

Although the astronaut feels weightless, that does not mean gravitational force is zero. Weightlessness in orbit occurs because the astronaut and satellite are in free fall together.

So option A is false.

  1. Compare with GMmR2\dfrac{GMm}{R^2}R2GMm​

Since h>0h>0h>0, we have

(R+h)2>R2.(R+h)^2>R^2.(R+h)2>R2.

Therefore,

GMm(R+h)2<GMmR2.\frac{GMm}{(R+h)^2}<\frac{GMm}{R^2}.(R+h)2GMm​<R2GMm​.

Also, gravitational force is clearly positive, so

0<GMm(R+h)2<GMmR2.0<\frac{GMm}{(R+h)^2}<\frac{GMm}{R^2}.0<(R+h)2GMm​<R2GMm​.

Hence option B is true.

  1. Check option C

Option C says

GMm(R+h)2<FG<GMmR2.\frac{GMm}{(R+h)^2}<F_G<\frac{GMm}{R^2}.(R+h)2GMm​<FG​<R2GMm​.

But we already found

FG=GMm(R+h)2.F_G=\frac{GMm}{(R+h)^2}.FG​=(R+h)2GMm​.

So the left inequality is not strict; it is actually equal. Therefore option C is false.

  1. Check option D

From the formula directly,

FG=GMm(R+h)2.F_G=\frac{GMm}{(R+h)^2}.FG​=(R+h)2GMm​.

So option D is true.

Final Answer

Correct options are B and D.

PreviousNext

More from Gravitation

  • A satellite is revolving in a circular orbit at a height ′h′ from the earth's surface (radius of earth R;h<<R). The minimum increase in its orbital velocity required, so that the satellite could escape from the earth's…2016 · MCQ
  • From a solid sphere of mass M and radius R, a spherical portion of radius R/2 is removed, as shown in the figure. Taking gravitational potential V=0 at r=∞, the potential at the center of the cavity thus formed is: (G=gravitationalconstant… Includes diagram2015 · MCQ
  • Four particles, each of mass M and equidistant from each other, move along a circle of radius R under the action of their mutual gravitational attraction. The speed of each particle is :2014 · MCQ
  • What is the minimum energy required to launch a satellite of mass m from the surface of a planet of mass M and radius R in a circular orbit at an altitude of 2R?2013 · MCQ
  • The mass of a spaceship is 1000kg. It is to be launched from the earth's surface out into free space. The value of g and R(radius of earth ) are 10m/s2 and 6400km respectively. The required energy for this work will be:2012 · MCQ
  • Two bodies of masses m and 4m are placed at a distance r. The gravitational potential at a point on the line joining them where the gravitational field is zero is:2011 · MCQ
  • The height at which the acceleration due to gravity becomes 9g​(where g= the acceleration due to gravity on the surface of the earth) in terms of R, the radius of the earth, is:2009 · MCQ
  • A planet in a distant solar system is 10 times more massive than the earth and its radius is 10 times smaller. Given that the escape velocity from the earth is 11kms−1, the escape velocity from the surface of the planet…2008 · MCQ