Here are Assertion-Reason Questions on Gravitation with answers and explanations for Class 11 CBSE Exam:
Assertion-Reason Questions on Gravitation
1.
Assertion (A): The acceleration due to gravity on the Moon is approximately 1/6 of that on Earth.
Reason (R): The Moon has a smaller mass and a smaller radius compared to Earth.
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.
Answer: A) Both A and R are true, and R is the correct explanation of A.
Explanation:
Acceleration due to gravity is given by:
\begin{array}{l} g = G \frac{M}{R^2} \end{array}
Since the Moon has much less mass than Earth and a smaller radius, the value of g is significantly lower.
2.
Assertion (A): The weight of an object is maximum at the poles and minimum at the equator.
Reason (R): The Earth’s rotation causes a centrifugal force that reduces effective gravity at the equator.
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.
Answer: A) Both A and R are true, and R is the correct explanation of A.
Explanation:
Due to Earth’s rotation, the centrifugal force acts outward and reduces the effective weight at the equator. This effect is absent at the poles.
3.
Assertion (A): The escape velocity from Earth is independent of the mass of the object.
Reason (R): Escape velocity is given by \begin{array}{l} v_e = \sqrt{\frac{2GM}{R}} \end{array}
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.
Answer: A) Both A and R are true, and R is the correct explanation of A.
Explanation:
Since the formula for escape velocity does not depend on the mass of the object, all objects have the same escape velocity from Earth.
4.
Assertion (A): The gravitational force between two objects becomes zero if the distance between them becomes infinite.
Reason (R): Gravitational force follows an inverse-square law.
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.
Answer: A) Both A and R are true, and R is the correct explanation of A.
Explanation:
From Newton’s Law of Gravitation:
\begin{array}{l} F = G \frac{m_1 m_2}{r^2} \end{array}
As r→∞r , F→0.
5.
Assertion (A): A satellite in a higher orbit around Earth has a greater speed than one in a lower orbit.
Reason (R): The orbital velocity is given by \begin{array}{l} v = \sqrt{\frac{GM}{R}} \end{array} , which decreases with an increase in R.
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 false, but R is true.
D) A is true, but R is false.
Answer: C) A is false, but R is true.
Explanation:
According to the orbital velocity formula, as R increases, v decreases, meaning satellites in higher orbits have lower speeds.
6.
Assertion (A): The gravitational potential energy of a body is negative.
Reason (R): The zero potential energy is taken at infinity, and work is required to move a mass away from a gravitational field.
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.
Answer: A) Both A and R are true, and R is the correct explanation of A.
Explanation:
Gravitational potential energy is given by:
\begin{array}{l} U = – G \frac{M m}{r} \end{array}
Since work is required to move a mass to infinity, U is negative.
7.
Assertion (A): The acceleration due to gravity at the center of the Earth is zero.
Reason (R): The gravitational force due to the mass of the Earth cancels out at the center.
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.
Answer: A) Both A and R are true, and R is the correct explanation of A.
Explanation:
At the center of the Earth, the gravitational forces from all directions cancel out, making g=0.
8.
Assertion (A): A geostationary satellite always appears fixed at a point in the sky.
Reason (R): The time period of a geostationary satellite is equal to Earth’s rotation period.
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.
Answer: A) Both A and R are true, and R is the correct explanation of A.
Explanation:
A geostationary satellite orbits Earth with a time period of 24 hours, keeping it fixed relative to Earth’s surface.
9.
Assertion (A): The Moon does not fall toward Earth due to gravity.
Reason (R): The Moon is in uniform circular motion around Earth.
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 false, but R is true.
D) A is true, but R is false.
Answer: C) A is false, but R is true.
Explanation:
The Moon is falling toward Earth but its tangential velocity keeps it in orbit, preventing it from crashing.
