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NEET Physics · Gravitation

Escape velocity and motion of satellites

Taught in NCERT Class 11 Physics, Chapter 7: Gravitation.

2 verified questions: Easy 0 · Medium 1 · NEET level 1

Sample questions

Sample 1Medium

Assertion (A): The escape speed of a body from Earth's surface depends on the mass of the body. Reason (R): The escape speed from Earth's surface is √(2GM/R), where M and R are the mass and radius of Earth.

  1. A

    Both Assertion and Reason are true, and Reason is the correct explanation of Assertion

  2. B

    Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion

  3. C

    Assertion is true, but Reason is false

  4. D

    Assertion is false, but Reason is true

Show the answer
The answer is D.

Equating ½mv² to GMm/R gives v = √(2GM/R). The mass m of the body cancels, so the assertion is false and the reason is true.

  • A.

    Assertion is false: the mass of the body cancels in ½mv² = GMm/R.

  • B.

    Assertion is false, so this pairing cannot hold.

  • C.

    Assertion is false, and Reason is true, so this option fails on both counts.

NCERT: Class 11 Physics, Chapter 7, Escape speed

Sample 2NEET level

A satellite moves in a circular orbit at a height equal to the radius of the earth above its surface. Taking the radius of the earth R = 6400 km and g = 10 m/s² at the surface, the orbital speed of the satellite is about

  1. A

    4.0 km/s

  2. B

    5.7 km/s

  3. C

    8.0 km/s

  4. D

    11.3 km/s

Show the answer
The answer is B.

Orbital speed v = √(GM/r) with r = 2R, and GM = gR², so v = √(gR/2) = √(10 × 6.4 × 10⁶ / 2) = √(3.2 × 10⁷) ≈ 5.7 × 10³ m/s. The orbit radius is measured from the earth's centre, not from the surface.

  • A.

    Uses g/4 at that height but keeps r = R: √(gR/4) = 4 km/s.

  • C.

    8 km/s is the orbital speed close to the earth's surface, √(gR).

  • D.

    11.3 km/s is the escape speed from the surface, √(2gR).

NCERT: Class 11 Physics, Chapter 7 (Gravitation), Earth satellites

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