Theme D: Fields

Two isolated point particles of mass 4M and 9M are separated by a distance 1m. A point particle of mass M is placed a distance x from the particle of mass 9M. The net gravitational force on M is zero. What is x?

• 1/4
• 1/2
• 2
• 4

Which graph shows the relationship between gravitational force F between two point masses and their separation r?

• A
• B
• C
• D

A planet has radius R. The escape speed from the surface of the planet is v. At what distance from the surface of the planet is the orbital speed 0.5v?

• 0.5R
• R
• 2R
• 4R

A satellite orbits planet X with a speed v_x at a distance r from the centre of planet X. Another satellite orbits planet Y at a speed of v_Y at a distance r from the centre of planet Y. The mass of planet X is M and the mass of m planet Y is 4M. What is the ratio of v_x : v_Y

• 0.25
• 0.5
• 2.0
• 4.0

A satellite of mass m orbits a planet of mass M in a circular orbit of radius r. What is the work that must be done on the satellite to increase its orbital radius to 2r?