Answer:
Newton's principle of force, the variation of the momentum and the acceleration have the same direction
Explanation:
To find the force exerted by the star on the sail of the ship, the expression of the momentum of the radiation is used, which in the case of a total reflection
p = [tex]\frac{2U}{c}[/tex]
where p is the momentum and U the incident energy and c the speed of light.
The strength I could get from
F = [tex]\frac{dp}{dt}[/tex]
the direction of the acceleration is the direction of the momentum, therefore the principle to find the acceleration of is Newton's principle of force, the variation of the momentum and the acceleration have the same direction.