Questions On Gravitation For Class 11 Pdf

Gravitation is a fundamental force of nature that governs the motion of celestial bodies and objects on Earth. It is one of the most important topics in Class 11 Physics, frequently asked in board exams and competitive tests like JEE, NEET, and Olympiads.

This topic covers important questions on gravitation, including conceptual, numerical, and application-based problems. It is structured to help students revise key concepts efficiently.

Understanding Gravitation

Before moving to the questions, let’s review some essential concepts:

1. Newton’s Law of Universal Gravitation
   • Every object attracts every other object with a force given by:
     F = G frac{m_1 m_2}{r^2}

     where:

     • F = gravitational force
     • G = universal gravitational constant ( $6.674 times 10^{-11} , Nm^2/kg2$ )
     • m_1, m_2 = masses of two objects
     • r = distance between their centers
2. Acceleration Due to Gravity (g)
   • The acceleration due to gravity on Earth is ** $9.8 m/s^2$ **.
   • It varies with height and depth using the formulas:
     g’ = g left( frac{R}{R+h} right)^2
     g’ = g left( 1 – frac{d}{R} right)
3. Kepler’s Laws of Planetary Motion
   • Law of Orbits: Planets move in elliptical orbits with the Sun at one focus.
   • Law of Areas: The area swept by the planet in equal time intervals is constant.
   • Law of Periods: The square of the orbital period is proportional to the cube of its semi-major axis.
4. Gravitational Potential Energy
   • The potential energy of an object at a distance r from a planet’s center is:
     U = – G frac{mM}{r}
5. Escape Velocity
   • The minimum velocity needed to escape Earth’s gravity is:
     v_e = sqrt{frac{2GM}{R}}

     For Earth, ** v_e = 11.2 km/s **.

6. Orbital Velocity
   • The velocity required to keep a satellite in orbit is:
     v_o = sqrt{frac{GM}{R}}

Conceptual Questions on Gravitation

Basic Questions

1. What is Newton’s Universal Law of Gravitation?
2. How does the gravitational force between two objects change if their distance is doubled?
3. What is the acceleration due to gravity on Earth?
4. Why do astronauts experience weightlessness in space?
5. What is the universal gravitational constant G ?
6. How does the gravitational force between two bodies depend on their masses?
7. What happens to the weight of an object as it moves from the equator to the poles?
8. Why does the Moon not fall into the Earth?
9. What is the difference between mass and weight?
10. How does g change with altitude and depth?

Application-Based Questions

1. Why do we weigh less on the Moon than on Earth?
2. How does Earth’s gravity affect satellite motion?
3. Why is escape velocity independent of the mass of the object?
4. What is a geostationary satellite?
5. What happens to a body’s weight at the center of the Earth?
6. How does the gravitational force between two objects change if one mass is doubled?
7. Why do planets move in elliptical orbits instead of circular ones?
8. How does the value of g vary on different planets?
9. What happens to Earth’s orbital speed if its distance from the Sun increases?
10. Why do astronauts need to wear heavy suits on the Moon?

Numerical Problems on Gravitation

Question 1: Gravitational Force Between Two Masses

Problem: Two masses of 5 kg and 10 kg are placed 2 meters apart. Find the gravitational force between them.

Solution:

Using the formula:

So, the force is ** $8.34 times 10^{-11} N$ **.

Question 2: Weight on the Moon

Problem: A person has a mass of 60 kg. What will be their weight on the Moon if the Moon’s gravity is ** $1/6$ **th of Earth’s?

Solution:

Weight is given by:

On Earth:

On the Moon:

So, the person’s weight on the Moon is 97.8 N.

Question 3: Escape Velocity on Mars

Problem: Find the escape velocity on Mars. Given:

• **Mass of Mars M = 6.42 times 10^{23} kg **
• **Radius of Mars R = 3.39 times 10^6 m **
• ** G = 6.674 times 10^{-11} Nm^2/kg^2 **

Solution:

Escape velocity formula:

So, the escape velocity on Mars is 5.03 km/s.

Common Misconceptions in Gravitation

1. Gravity exists only on Earth.
   • False! Gravity exists everywhere in the universe.
2. Mass and weight are the same.
   • No, mass is constant while weight depends on gravity.
3. There is no gravity in space.
   • Wrong! Gravity is present, but astronauts experience weightlessness due to free fall.
4. Larger planets always have higher gravity.
   • Not necessarily. Gravity depends on mass and radius.
5. Objects in orbit are beyond Earth’s gravity.
   • No, they are continuously falling but moving fast enough to stay in orbit.

Gravitation is a crucial topic in Class 11 physics, with applications in space science, astronomy, and engineering. By practicing conceptual and numerical problems, students can strengthen their understanding and prepare effectively for exams.

Regularly solving these questions will help in mastering gravitational concepts and applying them to real-world scenarios. Keep practicing and explore the fascinating world of physics!