Gravitation – Objective Questions
Page 3 • Tricky & Concept-Mixed Questions (With Explanations)
Question 15
Two bodies of masses m and 4m are placed at a distance r apart. The ratio of gravitational force exerted by the first body on the second to that exerted by the second on the first is:
A) 1 : 4 B) 4 : 1 C) 1 : 1 D) depends on distance
Correct Answer: C) 1 : 1
Explanation:
According to Newton’s third law, forces between two interacting bodies are equal in magnitude and opposite in direction.
Question 16
A body is taken to a depth equal to half the radius of Earth. The value of g at that point is:
A) g B) g/2 C) g/4 D) zero
Correct Answer: B) g/2
Explanation:
Inside Earth, g decreases linearly with depth:
gd = g(1 − d/R)
Here d = R/2 ⇒ gd = g/2
Question 17
Escape velocity of a planet depends on:
A) density of planet B) atmosphere of planet C) mass and radius of planet D) rotational speed of planet
Correct Answer: C) mass and radius of planet
Explanation:
ve = √(2GM/R). Only mass and radius of the planet matter.
Question 18
If Earth suddenly shrinks to half its radius without change in mass, escape velocity becomes:
A) half B) double C) √2 times D) four times
Correct Answer: B) double
Explanation:
ve ∝ 1/√R
If R → R/2, then ve → √2 ve.
But since ve = √(2GM/R), halving R doubles the value inside root,
so ve becomes √2 times.
(Exam Note: Options often confuse students—always substitute.)
Question 19
The weight of a satellite revolving around Earth is:
A) mg B) zero C) less than mg D) infinite
Correct Answer: B) zero
Explanation:
Satellite and astronaut both fall freely under gravity, so normal reaction is zero. Hence, weight is zero.
Question 20
A planet has the same mass as Earth but half its radius. Acceleration due to gravity on its surface will be:
A) g/2 B) g C) 2g D) 4g
Correct Answer: D) 4g
Explanation:
g = GM/R². If R → R/2 ⇒ g → 4g.
Question 21
Gravitational potential energy of a body at infinite distance from Earth is:
A) maximum B) minimum C) zero D) negative
Correct Answer: C) zero
Explanation:
Reference level of gravitational potential energy is taken as zero at infinity.
IIT Objective Solving Tip
Never assume answers by intuition. Always check how the quantity varies with R or M.
Objective Questions • Page 3 Completed ✅
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- Gravitation – Part 1
- Gravitation – Part 2
- Gravitation – Part 3
- Gravitation – Part 4
- Gravitation – Part 5
- Gravitation – Part 6
- Gravitation – Part 7
- Gravitation – Part 8
- Gravitation – Part 9
- Gravitation – Part 10
- Gravitation – Part 11
- Gravitation – Part 12
- Gravitation – Part 13
- Gravitation – Part 14
- Gravitation – Part 15
- Gravitation – Part 16
- Gravitation – Part 17
- Gravitation – Part 18
- Gravitation – Part 19
- Gravitation – Part 20
- Gravitation – Part 21
- Gravitation – Part 22
- Gravitation – Part 23
- Gravitation – Part 24
- Gravitation – Part 25
- Gravitation – Part 26
- Gravitation – Part 27
- Gravitation – Part 28
- Gravitation – Part 29
- Gravitation – Part 30
- Gravitation – Part 31
- Gravitation – Part 32
- Gravitation – Part 34
- Gravitation – Part 35
- Gravitation – Part 36
- Gravitation – Part 37
- Gravitation – Part 38
- Gravitation – Part 39
- Gravitation – Part 40
- Gravitation – Part 41
- Gravitation – Part 42
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