Gravitation

MCQs (Part I)

Question 1: A planet is moving in an elliptical orbit. If T, V, E and L are respectively the kinetic energy, potential energy, total energy and the magnitude of the angular momentum of the planet then the true statement out of the following is:

  1. T is conserved
  2. V is always positive
  3. E is always negative
  4. L is conserved but the direction vector continuously changes

Answer: (c) E is always negative

Question 2: The gravitational field in a region is given by N/kg then the magnitude of the gravitational force acting on a particle of mass 2 kg placed at the orgin, will be:

  1. zero
  2. 12 N
  3. 26 N
  4. 75 N

Answer: (c)26 N

Explanation: Given

Its magnitude

Thus,

= 13 × 2

= 26 N

Question 3: The minimum energy required to launch a m kg satellite from earth's surface in a circular orbit at an altitude of 2R where R is the radius of earth, will be:

  1. 3 mgR
  3. 2mgR

Answer: (b)

Question 4: The gravitational potential difference between the surface of a planet and a point 20 m above it is 16 J/kg. Then the work done in moving a 2 kg mass by 8 m on a slope 60º from the horizontal, is:

  1. 11.1 J
  2. 55.5 J
  3. 16 J
  4. 27.7 J

Answer: (a) 11.1 J

Question 5: Three particles, each of mass 10_2 kg are brought from infinity to the vertices of an equilateral triangle of side 0.1 m, the work done is:

  1. 2 × 10–8 J
  2. 2 × 10–11 J
  3. 2 × 10–12 J
  4. 2 × 10–13 J

Answer: (d) 2 × 10–13 J

Explanation: The work done in bringing each mass m from infinity to the vertices of equilateral triangle of side r is negative of the gravitational potential energy of the system.

W = – U

= 2 × 10–13 J

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