How Does Centripetal Force Relate to Distance in Orbital Motion?

[dance_sg]

Homework Statement

Newton showed that a centripetal force acts on an object moving in an orbit that varies

A. directly with the distance from the centre of force
B. inversely with the distance from the centre of force
C. directly with the square of the distance from the centre of force
D. inversely with the square of the distance form the centre of force







The question above is a question on the assignment that I am trying to finish. However, i do not understand what the question is asking, or what he answers mean. What is the square? and how do i know if its inversely or directly? ah! any suggestions??

 

[Feldoh]

directly with the square of distance = distance^2

inversely with the square of distance = 1/(distance^2)

 

[dance_sg]

ok. But how do i know if its inversly or directly? do i have to look at a formula?

 

[Feldoh]

Well what's Newtons law of gravity?

 

[cepheid]

ok. But how do i know if its inversly or directly? do i have to look at a formula?

You need to know HOW centripetal force varies with distance in order to answer the question (to pick the correct option). So yes, that would entail a formula for centripetal force that you ought to know.

EDIT: Okay, Feldoh interpreted "moving in an orbit" more narrowly that I did and assumed that the specific centripetal force in question was being caused by gravity. That could very well be what the question is asking about...

 

[dance_sg]

so since r is the distance between the two point masses in the formula, then that means it would d, inversely with the square of distance. right?

 

[cepheid]

Sounds about right.