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FIGURE 8–3 The gravitational force between any two bodies varies directly as the product of their masses and inversely as the square of the distance between them.£6.40
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FIGURE 8–3 The gravitational force between any two bodies varies directly as the product of their masses and inversely as the square of the distance between them.
FIGURE 8–3 The gravitational force between any two bodies varies directly as the product of their masses and inversely as the square of the distance between them.
MCQ I
8.1 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.
8.2 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.
20/04/2018
, Exemplar Problems–Physics
(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.
8.3 Different points in 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 c.m. (centre of mass) causing translation and a net torque
at the c.m. causing rotation around an axis through the c.m.
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.
8.4 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.
8.5 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.
8.6 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.
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20/04/2018
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