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## Homework Statement

A spaceship is flying in outer space, engines off. At a certain point A in space, the spaceship starts drifting sideways with a constant speed and in a straight line until it reaches a distant point B in space.

## Homework Equations

Which of the forces below may have caused the spaceship to move the way it did between points A and B?

F1: A force in the direction of motion exerted by some planets or other celestial objects

F2: A force in the direction of motion due to the original thrust of the spaceship

F3: An internal impulse developed gradually by the spaceship as it moves from A to B

A. F1.

B. F2.

C. F3.

D. Either one or a combination of the above three forces.

E. None. The spaceship can move the way it did between A and B without being driven by any internal or external force.

## The Attempt at a Solution

I first chose answer A, I wasn't paying attention. Now I know that an attraction force (F1) would at least be the same from point A to B so there would be acceleration an thus no constant speed. F2 and F3 aren't good as well. Answer D doesn't seem correct, so I've got option E left. However I cannot understand how this would be possible. Could someone give an explanation? Or maybe it isn't E...?

Thank you!