multiple choice physics question

Question

Which of the following is true about Newton's Universal Law of Gravity?

 A. It's essential to set m₁ equal to the mass of the lighter object and m₂ equal to the mass of the heavier object.

 B. If the separation between the masses increases by a factor of 4, the strength of the gravitational force between then decreases by a factor of 4.

 C. The heavier mass exerts a stronger gravitational force on the lighter mass.

 D. The strength of the gravitational force of object 1 on object 2 is equal to the strength of the gravitational force of object 2 on object 1.

Answer 1

Choice (d) is the correct answer.

However, please understand that unlike most other properties that belong to one object or another such as mass, velocity, momentum etc, Force does not belong to a single object and is always mutual BETWEEN two objects. In case of gravitational force, a single force exists between m₁ and m₂. In other words it is more appropriate to think of 1 attractive force between two masses rather than two equal forces, each exerted by a single object.

If you need further clarification, let me know.

Mr. A

Answer 2

(a) wrong, m1 and m2 are interchangeable

(b) wrong, gravitational force is proportional to 1/r², so if the separation increases x 4, force decreases by x 16

(c) No.

(d) True.

Mike