Q60. Why is the work done by gravity negative while a body is being lifted?
[RRB Group D — 18 Aug 2026, Shift 2]
(A) Gravity does positive work only in a fall
(B) The net force must be zero
(C) The magnitude of gravity changes
(D) The displacement is upward while gravity acts downward
Answer: (D) The displacement is upward while gravity acts downward
Explanation: Work is the scalar product of force and displacement. Lifting moves the body upward, whereas its gravitational force points downward. Their angle is 180 degrees, so W = Fs cos 180° is negative.
Q59. Why does a flat sheet of paper fall more slowly than a stone in air?
[SSC GD Constable — 26 May 2026, Shift 3]
(A) The objects experience different gravitational acceleration
(B) The paper encounters greater air resistance
(C) Only the difference in shape is relevant
(D) Gravity does not act on paper
Answer: (B) The paper encounters greater air resistance
Explanation: Air drag opposes the downward motion and has a larger effect relative to the weight of a flat sheet. In a vacuum, absent air resistance, a paper sheet and stone would have the same gravitational acceleration.
Q58. At the instant a body starts falling freely from rest at height h, which energy pair is correct?
[SSC GD Constable — 26 May 2026, Shift 3]
(A) Potential energy = 0; kinetic energy = mgh
(B) Potential energy = mgh; kinetic energy = 0
(C) Potential energy = ½mv²; kinetic energy = mgh
(D) Both potential and kinetic energy are zero
Answer: (B) Potential energy = mgh; kinetic energy = 0
Explanation: With the ground as the reference level, the elevated body has gravitational potential energy mgh. Because the fall starts from rest, speed is initially zero and kinetic energy is zero. During descent potential energy turns into kinetic energy.
Q57. Which kind of motion describes free fall near Earth when air resistance is ignored?
[RRB NTPC Graduate CBT-I — 17 Mar 2026, Shift 1]
(A) Uniformly accelerated motion
(B) Uniform motion
(C) Motion without acceleration
(D) Periodic motion
Answer: (A) Uniformly accelerated motion
Explanation: Near the surface, gravitational acceleration is nearly constant at about 9.8 m/s². Consequently, a freely falling body changes its velocity by equal amounts in equal intervals. That is uniformly accelerated motion, not motion at constant speed.
Q56. Taking upward as positive, what sign is used for acceleration in a vertically upward throw?
[RRB Technician Grade III — 06 Mar 2026, Shift 1]
(A) Negative
(B) Positive because gravity is constant
(C) Positive because the body rises
(D) The sign is unrelated to the chosen axis
Answer: (A) Negative
Explanation: The gravitational acceleration always points downward near Earth. If upward is designated the positive direction, downward acceleration is represented by −g. This sign convention yields v = u − gt and explains why the rising body slows down.
Q55. A stone falls freely from rest. Its motion is classified as which of these?
[RRB Group D — 05 Feb 2026, Shift 2]
(A) Non-uniform motion
(B) Straight-line motion with constant speed
(C) Motion with zero acceleration
(D) Uniform-velocity motion
Answer: (A) Non-uniform motion
Explanation: The stone travels increasingly large distances during successive equal time intervals because gravity increases its downward speed. Hence its speed is not uniform, although the downward acceleration is approximately constant in the near-surface region.
Q54. Assess the statements:
(i) g depends on the mass of the falling object;
ii) g is identical everywhere in the universe.
[RRB Group D — 04 Feb 2026, Shift 3]
(A) Only statement (i) is true
(B) Only statement (ii) is true
(C) Neither statement is true
(D) Both statements are true
Answer: (C) Neither statement is true
Explanation: The acceleration g depends on the attracting celestial body and the observation point, not the mass of the object being dropped. Since planetary masses and radii differ, gravity is not universally identical. Both proposed statements are therefore false.
Q53. Which formula expresses surface gravity using planetary mass M, radius R and universal constant G?
[RRB Group D — 04 Feb 2026, Shift 2]
(A) g = GR/M²
(B) g = R²/(GM)
(C) g = GM/R
(D) g = GM/R²
Answer: (D) g = GM/R²
Explanation: Newton’s gravitational law gives F = GMm/R² for a mass m on the surface. Newton’s second law gives F = mg. Equating and cancelling m produces g = GM/R², which decreases when the radius increases.
Q52. Just before a freely falling body reaches the ground, which energy condition applies?
[RRB Group D — 04 Feb 2026, Shift 1]
(A) Potential energy is maximum and kinetic energy minimum
(B) Potential and kinetic energies must be equal
(C) Kinetic energy is maximum and potential energy minimum
(D) Both energies necessarily become zero
Answer: (C) Kinetic energy is maximum and potential energy minimum
Explanation: Ignoring drag, the loss of gravitational potential energy equals the gain in kinetic energy. Close to ground level the body has its greatest speed and therefore maximum kinetic energy, while potential energy relative to the ground is lowest.
Q51. A planet has twice Earth’s mass and twice Earth’s radius. What is its surface gravitational acceleration?
[RRB Group D — 03 Feb 2026, Shift 2]
(A) 2g
(B) g/4
(C) g
(D) g/2
Answer: (D) g/2
Explanation: Surface gravity varies as M/R². With mass changing to 2M and radius to 2R, the new acceleration becomes G(2M)/(2R)² = GM/(2R²), precisely half Earth’s surface gravitational acceleration g.