K R Mangalam World School
South City I, Gurgaon
Grade XI
PHYSICS
CHAPTER 8 Gravitation
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MCQ
1. The weight of a body at the centre of the earth is
(a) Zero (b) Infinite (c) Same as on the surface of earth (d) None of the above
2. A body of mass m is taken to the bottom of a deep mine. Then
(a) Its mass increases (b) Its mass decreases (c) Its weight increases (d) Its weight decreases
3. At what altitude in metre will the acceleration due to gravity be 25% of that at the earth's surface (Radius of earth
= R metre)
(a) R/4 (b) R (c)3/8 R (d) R/2
4. Weight of a body of mass m decreases by 1% when it is raised to height h above the earth’s surface. If the body
is taken to a depth h in a mine, change in its weight is
(a) 2% decrease (b) 0.5% decrease (c) 1% increase (d) 0.5% increase
5. Energy required to move a body of mass m from an orbit of radius 2R to 3R is
(a) GMm/12R2(b)GMm/3R2 (c) GMm/8R (d) GMm/6R
6. Consider a satellite going round the earth in an orbit. Which of the following statements is wrong
(a) It is a freely falling body (b) It suffers no acceleration (c) It is moving with a constant speed (d) Its angular
momentum remains constant
7. Assuming the earth to have a constant density, point out which of the following curves show the variation of
acceleration due to gravity from the centre of earth to the points far away from the surface of earth
ASSERTION REASONING
Read the assertion and reason carefully to mark the correct option out of the options given below:
(a) If both assertion and reason are true and the reason is the correct explanation of the assertion. (b) If both
assertion and reason are true but reason is not the correct explanation of the assertion. (c) If assertion is true but
reason is false. (d) If the assertion and reason both are false. (e) If assertion is false but reason is true.
8. Assertion : Gravitational force between two particles is negligibly small compared to the electrical force.
Reason : The electrical force is experienced by charged particles only.
9. Assertion : The universal gravitational constant is same as acceleration due to gravity.
Reason : Gravitational constant and acceleration due to gravity have same dimensional formula.
10. Assertion : If a pendulum is suspended in a lift and lift is falling freely, then its time period becomes infinite.
Reason : Free falling body has acceleration equal to acceleration due to gravity.
1Mark Questions
1. The mass of moon is nearly 10% of the mass of the earth. What will be the gravitational force of the earth on the moon, in
comparison to the gravitational force of the moon on the earth ?
2. Why does one feel giddy while moving on a merry go round ?
3. Name two factors which determine whether a planet would have atmosphere or not.
4. The force of gravity due to earth on a body is proportional to its mass, then why does a heavy body not fall faster than a
lighter body ?
5. The force of attraction due to a hollow spherical shell of uniform density on a point mass situated inside is zero, so can a
body be shielded from gravitational influence ?
6. The gravitational force between two bodies in 1 N if the distance between them is doubled, what will be the force
between them ?
7. A body of mass 5 kg is taken to the centre of the earth. What will be its (i) mass, (ii) weight there.
8. Why is gravitational potential energy negative ?
9. A satellite revolves close to the surface of a planet. How is its orbital velocity related with escape velocity of that planet.
10. A satellite does not require any fuel to orbit the earth. Why ?
11. A satellite of small mass burns during its descent and not during ascent. Why ?
12. Is it possible to place an artificial satellite in an orbit so that it is always visible over New Delhi ?
2 Marks Questions
1. Draw graphs showing the variation of acceleration due to gravity with (i) height above earth is surface (ii) depth below the
earth’s surface.
2. A satellite is moving round the earth with velocity v0 what should be the minimum percentage increase in its velocity so
that the satellite escapes.
3. If earth has a mass 9 times and radius 4 times than that of a planet ‘P’. Calculate the escape velocity at the planet ‘P’ if its
value on earth is 11.2 kms–1.
4. At what height from the surface of the earth will the value of ‘g’ be reduced by 36% of its value at the surface of earth. 29.
At what depth is the value of ‘g’ same as at a height of 40 km from the surface of earth.
5. Why the space rockets are generally launched west to east ?
6. Calculate the energy required to move a body of mass m from an orbit of radius 2R to 3R.
3 Marks Questions
1. Find the potential energy of a system of four particles, each of mass m, placed at the vertices of a square of side. Also
obtain the potential at the centre of the square.
2. Three mass points each of mass m are placed at the vertices of an equilateral triangle of side I. What is the gravitational
field and potential at the centroid of the triangle due to the three masses.
3.The escape velocity of a projectile on earth’s surface is 11.2 kms–1. A body is projected out with thrice this speed. What is
the speed of the body far away from the earth ? Ignore the presence of the sun and other planets.
