Physics NCERT Exemplar Solutions Class 11th Chapter Eight

If the law of gravitation, instead of being inverse-square law, becomes an inverse-cube law-

(a) Planets will not have elliptic orbits.

(b) Circular orbits of planets is not possible.

(c) Projectile motion of a stone thrown by hand on the surface of the earth will be approximately parabolic.

(d) There will be no gravitational force inside a spherical shell of uniform density.

Which of the following options are correct?

(a) Acceleration due to gravity decreases with increasing altitude.

(b) Acceleration due to gravity increases with increasing depth (assume the earth to be a sphere of uniform density).

(c) Acceleration due to gravity increases with increasing latitude.

(d) Acceleration due to gravity is independent of the mass of the earth.

Particles of masses 2M, m and M are respectively at points A, B and C with AB = ½ (BC). m is much-much smaller than M and at time t = 0, they are all at rest (Fig. 8.1). At subsequent times before any collision takes place:

(a) m will remain at rest.

(b) m will move towards M.

(c) m will move towards 2M.

(d) m will have oscillatory motion.

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 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.

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 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.

Both earth and 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 earth.

Satellites orbiting 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.

As observed from earth, the sun appears to move in an approximate circular orbit. For the motion of another planet like mercury as observed from earth, this would

(a) Be similarly true.

(b) Not be true because the force between earth and mercury is not inverse square law

(c) Not be true because the major gravitational force on mercury is due to sun.

(d) Not be true because mercury is influenced by forces other than gravitational forces.

The earth is an approximate sphere. If the interior contained matter which is not of the same density everywhere, then on the surface of the earth, the acceleration due to gravity

(a) Will be directed towards the centre but not the same everywhere.

(b) Will have the same value everywhere but not directed towards the centre.

(c) Will be same everywhere in magnitude directed towards the centre.

(d) Cannot be zero at any point.