- #1

- 354

- 0

## Homework Statement

How would I go about finding the time it takes for a particle of mass [tex]m[/tex] to travel in a straight line only under the force of gravity between any two points on the surface of a solid sphere of mass [tex]M[/tex].

## Homework Equations

[tex]\mathbf{F}=-{3GM \over R^3} \matbhf{r}[/tex] (I derived this using integration and Newton's Universal Law of Gravitation)

## The Attempt at a Solution

Don't tell me how to do it, just give me a hint. I think what's really tripping me up here is how do you have an object traveling along a non-field-line curve

*only*under the force of gravity? Wouldn't there have to be some normal force keeping the object on the curve?