question_answer

Which of the following observations point to the equivalence of inertial and gravitational mass: (a) Two spheres of different masses dropped from the top of a long evacuated tube reach the bottom of the tube at the same time. (b) The time-period of a simple pendulum is independent of its mass. (c) The gravitational force on a particle inside a hollow isolated sphere is zero. (d) For a man in closed cabin that is falling freely under gravity, gravity 'disappears'. (e) An astronaut inside a spaceship orbiting around the Earth feels weightless. (f) Planets orbiting around the sun obey Kepler's Third Law (approximately). (g) The gravitational force on a body due to the Earth is equal and opposite to the gravitational force on the Earth due to the body.                                 

Answer:

                The observations (a), (b), (d (e) and (f) point to the equivalence of gravitational masses, because in these situations the bodies are in motion.                     The observations (c) and (g) do not establish the equivalence of inertial and gravitational masses because the bodies are not in the state of motion.