Class Notes NCERT Solutions for CBSE Students
ST MARGARET SR SEC. SCHOOL
PT–II EXAMINATION 2025–26
| Subject: | Physics |
| Class: | XI |
| Set: | SET – B |
| Time: | 01 Hour |
| Maximum Marks: | 25 |
General Instructions:
- All questions are compulsory.
- The question paper consists of Sections A, B, C, D and E.
- Internal choices are provided wherever applicable.
- Use of a calculator is not permitted.
SECTION – A (Multiple Choice Questions)
Q1. Two satellites, P and Q, revolve around the Earth in the same circular orbit. The mass of satellite P is greater than that of satellite Q. Which of the following statements is correct?
- (a) The speed of P is equal to the speed of Q
- (b) The speed of P is greater than the speed of Q
- (c) The speed of P is less than the speed of Q
- (d) The kinetic energy of P is equal to the kinetic energy of Q
Q2. The mass of the Moon is 1% of the mass of the Earth. The ratio of the gravitational pull of the Earth on the Moon to the gravitational pull of the Moon on the Earth is
- (a) 1 : 1
- (b) 1 : 10
- (c) 1 : 100
- (d) 2 : 1
Q3. Assertion (A): Kepler’s Second Law can be explained on the basis of the Law of Conservation of Angular Momentum.
Reason (R): The areal velocity of a planet remains constant because its angular momentum remains conserved.
- (a) Both A and R are true and R is the correct explanation of A
- (b) Both A and R are true but R is not the correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true
Q4. Assertion (A): Torque on a body may be zero even when the net force acting on the body is not zero.
Reason (R): Force and torque acting on a body are always perpendicular to each other.
- (a) Both A and R are true and R is the correct explanation of A
- (b) Both A and R are true but R is not the correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true
SECTION – B (2 Marks Each)
Q5. A satellite is revolving around the Earth with orbital speed v₀. What minimum percentage increase in its velocity is required so that it escapes from the gravitational field of the Earth?
Q6. A body of mass M is broken into two parts of masses m₁ and m₂. How should m₁ and m₂ be related so that the gravitational force of attraction between them is maximum?
Q7. A force F = 2i − 3j − 4k acts on a particle at a point whose position vector is r = 3i − 2j + 3k (in SI units). Find the torque of this force about the origin.
SECTION – C (3 Marks Each)
Q8. Two rotating bodies, A and B, have moments of inertia Iₐ and Iᵦ, respectively, such that Iₐ > Iᵦ. If both bodies have equal angular momenta, which body will possess greater rotational kinetic energy? Justify your answer.
SECTION – D (4 Marks)
Q9. Three particles, each of mass m, are placed at the vertices of an equilateral triangle of side l. Calculate:
(a) the gravitational field intensity at the centroid of the triangle, and
(b) the gravitational potential at the centroid.
Q10. The rate of change of total angular momentum of a system is equal to the sum of the external torques acting on the system.
Answer the following:
(i) In which physical situations is the law of conservation of angular momentum applicable?
(ii) What condition must be satisfied for angular momentum to remain conserved?
(iii) A person standing on a frictionless rotating stool stretches his arms outward and then pulls them inward. What happens to his moment of inertia and angular velocity in each case?
(iv) Two children, Ram and Raj, are sitting on a rotating merry-go-round. Ram is seated farther from the axis of rotation than Raj. Who will have the greater linear speed? Give a reason.
SECTION – E (5 Marks)
Q11. (a) At what height above the surface of the Earth will the value of acceleration due to gravity become half of its value on the Earth’s surface? (Take radius of Earth R = 6400 km.)
(b) At what depth below the surface of the Earth will the value of g be:
(i) 36% of its surface value?
(ii) reduced by 36% of its surface value?
