"We observe a very small moon orbiting a planet and measure the moon's min. and max. distances from the planet's center, and the moon's maximum orbital speed. Which of the following CANNOT be measured?"
A) Mass of moon
B) Mass of planet
C) Minimum Speed of the moon
D) Period of the orbit
E) Semimajor axis of the orbit
Based on Kepler's third law, we can calculated D) and E). From this, it's not impossible to measure C).
But how would I go about calculating the planet itself from these measurements?
The correct answer is apparently A), because "an object in free fall in a vacuum will fall at the same acceleration regardless of its mass." Here, space is the vacuum.