Q 1 :

Match List-I with List-II                                                              [2024]

  List - I   List - II
A Kinetic energy of planet (I) -GMm/a
B Gravitation Potential energy of sun planet system (II) GMm/2a
C Total mechanical energy of planet (III) GMm/r
D Escape energy at the surface of planet for unit mass object (IV) -GMm/2a

 

  • (A)-(I), (B)-(IV), (C)-(II), (D)-(III)

     

  • (A)-(II), (B)-(I), (C)-(IV), (D)-(III)

     

  • (A)-(III), (B)-(IV), (C)-(I), (D)-(II)

     

  • (A)-(I), (B)-(II), (C)-(III), (D)-(IV)

     

(2)   

       Potential energy = -GMma

        Total energy = -GMm2a

        kinetic energy = GMmr

       Escape energy = GMmr

 



Q 2 :

To project a body of mass m from earth's surface to infinity, the required kinetic energy is (assume, the radius of earth is RE) g = acceleration due to gravity on the surface of earth:              [2024]

  • mgRE

     

  • 1/2mgRE

     

  • 4mgRE

     

  • 2mgRE

     

(1)   

        Escape speed ve=2GMRE

        Escape kinetic energy Ke=12mve2

        Ke=12m(2GMRE)2=GMmRE

         Also, GM=gRE2Ke=(gRE2)mRE=mgRE

 



Q 3 :

An astronaut takes a ball of mass m from earth to space. He throws the ball into a circular orbit about earth at an altitude of 318.5 km. From earth's surface to the orbit, the change in total mechanical energy of the ball is xGMem21Re. The value of x is (take Re= 6370 km):                          [2024]

  • 11

     

  • 9

     

  • 12

     

  • 10

     

(1) 

        h=318.5(Re20)

        T·Ei=-GMemRe

        T·Ef=-GMem2(Re+h)=-GMem2(Re+Re20)

        Change in total mechanical energy = TEf-TEi

         =GMemRe[1-1021]=11GMem21Ren

 



Q 4 :

The gravitational potential at a point above the surface of earth is -5.12×107 J/kg and the acceleration due to gravity at that point is 6.4 m/s2.     

Assume that the mean radius of earth to be 6400 km. The height of this point above the earth's surface is:                      [2024]

  • 1600 km

     

  • 540 km

     

  • 1200 km

     

  • 1000 km

     

(1)  

      Vg=-GM(R+h)=-5.12×107 J/kg

       g=GM(R+h)2=6.4m/s2

       Vgg=-(R+h)

       -5.12×1076.4=-(R+h)

         6400 km + h = 8000 km

         h = 1600 km

 



Q 5 :

Escape velocity of a body from earth is 11.2 km/s. If the radius of a planet be one-third the radius of earth and mass be one-sixth that of earth, the escape velocity from the planet is                        [2024]

  • 11.2 km/s

     

  • 8.4 km/s

     

  • 4.2 km/s

     

  • 7.9 km/s

     

(4) 

       RP=RE3, MP=ME6

        Ve=2GMR for earth

         Ve'=2G(M/6)(R/3)=GMR for planet

        2Ve'=Ve

         Ve'=Ve2=11.22=(11.2)×0.7 km/sec

         Ve'=7.84 km/sec7.9km/sec

 



Q 6 :

The mass of the moon is 1/144 times the mass of a planet and its diameter 1/16 times the diameter of a planet. If the escape velocity on the planet is V, the escape velocity on the moon will be                 [2024]

  • V/3

     

  • V/4

     

  • V/12

     

  • V/6

     

(1) 

        Vescape=2GMR

         Vplanet=2GMR=V

          VMoon=2GM×16144R=132GMR

         VMoon=VPlanet3=V3

 



Q 7 :

A satellite of 103 kg mass is revolving in a circular orbit of radius 2R. If 104R6J energy is supplied to the satellite, it would revolve in a new circular orbit of radius: (use g = 10 m/s2, R = radius of Earth)         [2024]

  • 2.5 R

     

  • 3 R

     

  • 4 R

     

  • 6 R

     

(4)

Total energy=-GMm2(2R)

If energy =104R6 is added then,

-GMm4R+104R6=-GMm2r, where r is new radius of revolving

-mgR4+104R6=-mgR22r, As g=GMR2

-103×10×R4+104R6=-103×10×R22r

-14+16=-R2rr=6R



Q 8 :

Earth has mass 8 times and radius 2 times that of a planet. If the escape velocity from the earth is 11.2 km/s, the escape velocity in km/s from the planet will be :          [2025]

  • 11.2

     

  • 5.6

     

  • 2.8

     

  • 8.4

     

(2)

vescape=2GMR; Mearth=8Mplanet; Rearth=2Rplanet

vplanetvearth=MplanetMearth×RearthRplanet

vplanet=(11.2 km/s)18×2=5.6 km/s



Q 9 :

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R

Assertion A : The kinetic energy needed to project a body of mass m from earth surface to infinity is 12mgR, where R is the radius of earth.

Reason R : The maximum potential energy of a body is zero when it is projected to infinity from earth surface.

in the light of the above statements, choose the correct answer from the options given below          [2025]

  • A is false but R is true

     

  • Both A and R are true and R is the correct explanation of A

     

  • A is true but R is false

     

  • Both A and R are true but R is NOT the correct explanation of A

     

(1)

At , PE is zero, U = 0

12mv2GMmR=0

KE=GMR2·mR=mgR



Q 10 :

An object is kept at rest at a distance of 3R above the earth's surface where R is earth's radius. The minimum speed with which it must be projected so that it does not return to earth is: (Assume M = mass of earth, G = Universal gravitational constant)          [2025]

  • GM2R

     

  • GMR

     

  • 3GMR

     

  • 2GMR

     

(1)

KEi+PEi=KEg+PEg

12mv2GMm4R=0+0

v2=GMR12  v=GM2R



Q 11 :

Two particles of equal mass 'm' move in a circle of radius 'r' under the action of their mutual gravitational attraction. The speed of each particle will be     [2023]

  • GM2r

     

  • 4GMr

     

  • GMr

     

  • GM4r

     

(4)

Gm24r2=mv2rv=Gm4r



Q 12 :

A body of mass m is taken from Earth’s surface to the height h equal to twice the radius of Earth (Re), the increase in potential energy will be: (g = acceleration due to gravity on the surface of Earth)            [2023]

  • 12mgRe

     

  • 3mgRe

     

  • 23mgRe

     

  • 13mgRe

     

(3)

U=-GMemr and Ui=-GMemRe

Uf=-GMem(Re+h)=-GMemRe+2Re=-GMem3Re

Increase in internal energy ΔU=Uf-Ui

       =23GMemRe

=23GMeRe2mRe=23mgRe



Q 13 :

If the gravitational field in space is given as (-Kr2) Taking the reference point to be at r=2 cm with gravitational potential V=10 J/kg, find the gravitational potential at r = 3 cm in SI unit. (Given that K = 6 J cm/kg)                   [2023]

  • 9

     

  • 11

     

  • 12

     

  • 10

     

(2)

-dVdr=-kr2  10VdV=23kr2dr

V-10=k[12-13]

V-10=k6  V=11 volts



Q 14 :

An object is allowed to fall from a height R above the Earth, where R is the radius of the Earth. Its velocity when it strikes the Earth's surface, ignoring air resistance, will be          [2023]

  • 2gR

     

  • gR

     

  • gR2

     

  • 2gR

     

(2)

Loss in PE = Gain in KE

(-GMm2R)-(-GMmR)=12mv2

v2=GMR=gR

v=gR



Q 15 :

If Earth has a mass nine times and radius twice to that of a planet P. Then ve3x ms-1 will be the minimum velocity required by a rocket to pull out of gravitational force of P, where ve is escape velocity on Earth. The value of x is                      [2023]

  • 2

     

  • 3

     

  • 18

     

  • 1

     

(1)

v(escape)planet=2GMpRp

                        =2G(Me9)(Re2)=ve23

  x=2



Q 16 :

The escape velocities of two planets A and B are in the ratio 1 : 2. If the ratio of their radii respectively is 1 : 3, then the ratio of acceleration due to gravity of planet A to the acceleration of gravity of planet B will be          [2023]

  • 43

     

  • 32

     

  • 23

     

  • 34

     

(4)

 



Q 17 :

Given below are two statements: one is labelled as Assertion A and the other is labelled as Reason R.            [2023]

Assertion A: Earth has atmosphere whereas moon doesn’t have any atmosphere.

Reason R: The escape velocity on moon is very small as compared to that on earth.

In the light of the above statements, choose the correct answer from the options given below:

  • A is true but R is false

     

  • Both A and R are correct but R is NOT the correct explanation of A

     

  • Both A and R are correct and R is the correct explanation of A

     

  • A is false but R is true

     

(3)

At Moon, due to low escape velocity, the rms velocity of molecules is greater than escape velocity. Hence molecules escape and there is no atmosphere at Moon.



Q 18 :

If V is the gravitational potential due to a sphere of uniform density on its surface, then its value at the center of the sphere will be               [2023]

  • 3V2

     

  • V

     

  • 43V

     

  • V2

     

(1)

V=GM2R3(3R2-r2) at r=RV=(GMR)

At r=0,V0=3GM2R=(3V2)



Q 19 :

A spaceship of mass 2×104 kg is launched into a circular orbit close to the Earth’s surface. The additional velocity to be imparted to the spaceship in the orbit to overcome the gravitational pull will be (if g=10 m/s2 and radius of Earth = 6400 km)                  [2023]

  • 11.2(2-1) km/s

     

  • 7.9(2-1) km/s

     

  • 8(2-1) km/s

     

  • 7.4(2-1) km/s

     

(3)

vorbit=GMR=gR

vescape=2GMR=2gR

Δv=(2-1)gR=8(2-1) km/s



Q 20 :

The ratio of escape velocity of a planet to the escape velocity of Earth will be:

Given: Mass of the planet is 16 times the mass of Earth and radius of the planet is 4 times the radius of Earth.          [2023]

  • 4 : 1

     

  • 2 : 1

     

  • 1 : 2

     

  • 1 : 4

     

(2)

vescape=2GMR

 vescape for planet =2G(16ME)4RE=22GMERE

                                         =2(vescape for Earth)



Q 21 :

A planet having mass 9Me and radius 4Re, where Me and Re are mass and radius of Earth respectively, has escape velocity in km/s given by: (Given escape velocity on Earth Ve=11.2×103 m/s)                        [2023]

  • 67.2

     

  • 16.8

     

  • 33.6

     

  • 11.2

     

(2)

VP=2GMPRP, VE=2GMERE

VPVE=2GMPRP2GMERE=RERP×MPME

VP=14×9×VE=32VE

VP=32×11.2 km/sec=16.8 km/sec



Q 22 :

Given below are two statements:                               [2023]

Statement I: For a planet, if the ratio of mass of the planet to its radius increases, the escape velocity from the planet also increases.

Statement II: Escape velocity is independent of the radius of the planet.

In the light of above statements, choose the most appropriate answer from the options given below:

  • Both Statement I and Statement II are incorrect

     

  • Statement I is correct but Statement II is incorrect

     

  • Statement I is incorrect but Statement II is correct

     

  • Both Statement I and Statement II are correct

     

(2)

Ve=2GMRVeMR

As MR increases Ve increases

Statement (1) is correct

Also, Ve1R

As Ve depends upon R 

 Statement (2) is incorrect



Q 23 :

A body is released from a height equal to the radius (R) of the Earth. The velocity of the body when it strikes the surface of the Earth will be (Given g = acceleration due to gravity on the Earth.)                    [2023]

  • gR

     

  • 4gR

     

  • 2gR

     

  • gR2

     

(1)

By conservation of mechanical energy

Ui+Ki=Uf+Kf

         -GMm2R+0=-GMmR+12mv2

GMm2R=12mv2

v=GMR=gR



Q 24 :

Three masses 200 kg, 300 kg and 400 kg are placed at the vertices of an equilateral triangle with side 20 m. They are rearranged on the vertices of a bigger triangle of side 25 m and with the same centre. The work done in this process is __________ J.  

(Gravitational constant G=6.7×10-11 N m2/kg2)                                   [2026]

  • 2.85×10-7

     

  • 1.74×10-7

     

  • 9.86×10-6

     

  • 4.77×10-7

     

(2)

Work done by external agent:

Wext=ΔU

Ui=-Gm1m2ri-Gm2m3ri-Gm1m3ri : ri=20 m

Uf=-Gm1m2rf-Gm2m3rf-Gm1m3rf : rf=25 m

Ui=-6.67×10-1120[200×300+300×400+200×400]

    =-6.67×10-1120×26×104=-86.71×10-8 J

Uf=-6.67×10-1125[200×300+300×400+200×400]

=-6.67×10-1125×26×104=-693.68×10-9

=-69.36×10-8 J

ΔU=Uf-Ui=1.74×10-7 J



Q 25 :

The escape velocity from a spherical planet A is 10 km/s. The escape velocity from another planet B whose density and radius are 10% of those of planet A, is ____ m/s.     [2026]
 

  • 2005

     

  • 1000

     

  • 10010

     

  • 10002

     

(3)

Ve=2GMR=2G×ρ×4πR33RVeρ×R

(Ve)B(Ve)A=ρBρA×RBRA=0.1ρAρA×(0.1RARA)

(Ve)B(Ve)A=110×110

(Ve)B=10×10001010=10010 m/sec



Q 26 :

Two identical spherically symmetric planets, each of mass M, are somehow held at rest with respect to each other. Each planet has radius R, and the distance between the centers of the planets is 4R. If a rocket is launched from the surface of one planet with speed v, what is the minimum speed v so that the rocket can reach the other planet?

  • 2GMR

     

  • GMR

     

  • 3GM4R

     

  • 2GM3R

     

(4)

The gravitational force vanishes at the midway point between the planets, so the rocket only needs to have enough energy to get there. The initial and final gravitational potential energies are Ui=-GMmR-GMm3R=-4GMm3R and Uf=-2GMm2R=-GMmR