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3
MCQ (Single Correct Answer)

Different points in the earth are at slightly different distances from the sun and hence experience different forces due to gravitation. For a rigid body, we know that if various forces act at various points in it, the resultant motion is as if a net force acts on the CM (centre of mass) causing translation and a net torque at the CM causing rotation around an axis through the CM. For the earth-sun system (approximating the earth as a uniform density sphere).

A
the torque is zero
B
the torque causes the earth to spin
C
the rigid body result is not applicable since the earth is not even approximately a rigid body
D
the torque causes the earth to move around the sun
4
MCQ (Single Correct Answer)

Satellites orbitting the earth have finite life and sometimes debris of satellites fall to the earth. This is because

A
the solar cells and batteries in satellites run out
B
 the laws of gravitation predict a trajectory spiralling inwards
C
of viscous forces causing the speed of satellite and hence height to gradually decrease
D
of collisions with other satellites
5
MCQ (Single Correct Answer)

Both the earth and the moon are subject to the gravitational force of the sun. As observed from the sun, the orbit of the moon

A
will be elliptical
B
will not be strictly elliptical because the total gravitational force on it is not central
C
is not elliptical but will necessarily be a closed curve
D
deviates considerably from being elliptical due to influence of planets other than the earth
6
MCQ (Single Correct Answer)

In our solar system, the inter-planetary region has chunks of matter (much smaller in size compared to planets) called asteroids. They

A
will not move around the sun, since they have very small masses compared to the sun
B
will move in an irregular way because of their small masses and will drift away into outer space
C
will move around the sun in closed orbits but not obey Kepler's laws
D
will move in orbits like planets and obey Kepler's laws
7
MCQ (Single Correct Answer)

Choose the wrong option.

A
Inertial mass is a measure of difficulty of accelerating a body by an external force whereas the gravitational mass is relevant in determining the gravitational force on it by an external mass
B
That the gravitational mass and inertial mass are equal is an experimental result
C
That the acceleration due to gravity on the earth is the same for all bodies is due to the equality of gravitational mass and inertial mass
D
Gravitational mass of a particle like proton can depend on the presence of neighbouring heavy objects but the inertial mass cannot
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