SAT Gravity- Gravity, orbits and circular motion

page 1


Section A

The following statements relate to the numbered questions 1-3 below. Each choice may be used once, several times, or not at all:

  • A) the same
  • B) 2 times larger
  • C) 4 times larger
  • D) 8 times larger
  • E) 16 times larger


1. The gravitational force between two objects of mass M and m seperated by a distance r is F. If the distance is decreased to r/2 and the mass M increased to 4M, how does the new force compare to F?

2. Two satellites X and Y are in orbit around the Earth at the same distance. Satellite X is has twice the mass of satellite Y. How large is the time period for 1 orbit of X compared to the time period for satellite Y?

3. Two small masses m and 2m are located at distances r and 2r from a much larger planet as shown.


How strong is the gravitational field strength at m compared to the gravitational field strength at 2m?


Section B

4. All three masses in the above diagram (question 3) will be attracted together. Which mass - if any - moves with the largest initital acceleration?

  • A) planet
  • B) mass m
  • C) mass 2m
  • D) mass m and 2m have the same high acceleration
  • E) none accelerate - they all have a constant velocity


5. Newton's Law of gravitation states (in part) that the force between two masses is

  • A) proportional to the square of the distance between them
  • B) proportional to the sum of the masses
  • C) inversely proportional to the square of the distance between them
  • D) inversely proportional to the product of the masses
  • E) inversely proportional to the distance between them


6. The gravitational field strength is defined as the

  • A) work done per unit mass getting to that point from infinity
  • B) force per unit distance
  • C) acceleration of gravity
  • D) acceleration per unit mass
  • E) force per unit mass


7. The diagram shows a planet and a moon . At approximately which point will the gravitational field strength between the planet and moon be zero?

8. Mars takes longer to orbit the Sun than the Earth. Which of these statements about Mars' orbit is true?

The circumference of Mars' orbit is longer than that of the Earth
Mars orbits at a slower velocity than the Earth
The centripetal force acting on Mars is smaller than that on the Earth
  • A) II only
  • B) I and II
  • C) I and III
  • D) II and III
  • E) All three statements