Gravitation — Class 11 MCQs with Answers

Gravitation — important questions & MCQs with answers (Class 11 Physics)

6 solved questions from this chapter's difficulty levels, each with its answer and explanation. Tap an option to check yourself.

0 of 6 answered

1. Q1 of 6Easy

   Newton's law of gravitation: F =

   AGm₁m₂rBGm₁m₂/rCGm₁m₂/r²DG/(m₁m₂r²)
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   Answer: Gm₁m₂/r²

   Explanation: Newton's law of gravitation is inverse-square: F = Gm₁m₂/r². Writing Gm₁m₂r or dropping the square on r is the classic slip — check that r sits squared in the denominator, not the numerator.

2. Q2 of 6Easy

   Newton's law of gravitation: F =

   Am₁ + m₂BG m₁m₂/rCG/(m₁m₂)DG m₁m₂/r²
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   Answer: G m₁m₂/r²

   Explanation: Newton's law of gravitation: F = Gm₁m₂/r², the inverse-square law. G/(m₁m₂) inverts the masses and drops r² — force must scale directly with each mass, not inversely.

3. Q3 of 6Medium

   g at height 6400 km (= R) above Earth (R = 6400 km):

   Ag/16Bg/2CgDg/4
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   Answer: g/4

   Explanation: At height h = R (total distance 2R from center), g_h = gR²/(R+h)² = gR²/(2R)² = g/4. Writing g/2 mistakes the squared denominator for a linear one — always square the (R+h) term first.

4. Q4 of 6Medium

   Escape velocity from planet of mass M and radius R:

   A√GMrB√(GM/R)C√(2GM/R)DGMR
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   Answer: √(2GM/R)

   Explanation: Escape velocity is v = √(2GM/R), from setting ½mv² = GMm/R. Omitting the 2, as in √(GM/R), instead gives the orbital velocity at the surface — a factor-of-2 slip that is the most common trap in this topic.

5. Q5 of 6Hard

   For satellite at radius r orbiting Earth, ratio of escape velocity from that point to its orbital velocity:

   A1B√2C2D1/2
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   Answer: √2

   Explanation: At any orbital radius, v_esc = √(2GM/r) and v_orb = √(GM/r), so v_esc/v_orb = √2 ≈ 1.41. Picking a ratio of 2 confuses the velocity ratio with the energy ratio, since kinetic energy scales as velocity squared.

6. Q6 of 6Hard

   Orbital velocity depends on:

   ACentral body's mass and the orbit radiusBMass of satelliteCMass of bothDVariable
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   Answer: Central body's mass and the orbit radius

   Explanation: Orbital velocity v = √(GM/r) depends only on the central body's mass M and orbital radius r — the satellite's own mass cancels out of GMm/r² = mv²/r. Picking 'mass of satellite' ignores this cancellation in the force balance.

Gravitation notes: key concepts (Class 11 Physics)

Newton's universal law of gravitation and everything it explains: how g depends on altitude, depth and latitude, gravitational potential and potential energy, escape and orbital velocities, the energy of a bound satellite, Kepler's three laws of planetary motion, and the true cause of weightlessness in orbit.

Universal law of gravitation

Every pair of masses attracts along the line joining them with a force proportional to the product of masses and inversely proportional to the square of the separation.

Gravitational constant G

A true universal constant, 6.67 × 10⁻¹¹ N m² kg⁻², identical everywhere. Unlike g it does not change with location, altitude or the body considered.

Acceleration due to gravity

The acceleration of a freely falling body, g = GM/R², around 9.8 m s⁻² at Earth's surface. It is a property of the planet, not of the falling body.

Variation of g with altitude

g falls off as you rise, roughly as g(1 − 2h/R) for heights small compared with Earth's radius, and as an inverse square at large distances.

Variation of g with depth

g decreases linearly going down and reaches exactly ZERO at the centre of the Earth, because only the mass in the sphere below you contributes.

Variation of g with latitude

Earth's rotation reduces the effective g most at the equator and not at all at the poles, so a body weighs slightly less at the equator.

Gravitational field intensity

The gravitational force per unit mass at a point, E = GM/r². It is a vector field pointing towards the attracting mass.

Gravitational potential

The potential energy per unit mass, V = −GM/r. It is negative everywhere and rises to zero only at infinite separation.

Gravitational potential energy

For two masses it is −Gm₁m₂/r. The negative sign encodes that the system is BOUND — work must be supplied to separate the masses.

Escape velocity

The minimum launch speed for a body to escape a planet's gravity without further propulsion, about 11.2 km s⁻¹ for Earth. It is independent of the body's mass.

Orbital velocity

The speed needed to stay in a circular orbit of radius r, √(GM/r). It decreases for higher orbits, so distant satellites move more slowly.

Energy of a satellite

The total energy of a bound satellite is negative, −GMm/2r, being the sum of positive kinetic and larger-magnitude negative potential energy.

Geostationary satellite

Orbits in Earth's equatorial plane with a 24-hour period at about 36,000 km altitude, so it appears fixed overhead — the basis of communication satellites.

Polar satellite

Orbits at low altitude passing over the poles, so the rotating Earth presents a new strip on each pass. Used for remote sensing and weather imaging.

Kepler's laws

Planets move in ellipses with the Sun at one focus; the radius vector sweeps equal areas in equal times; and the square of the period is proportional to the cube of the semi-major axis.

Weightlessness

Occurs in free fall, not in the absence of gravity. An orbiting astronaut is falling continuously with their spacecraft, so the normal force between them is zero.