A 160.-kilogram space vehicle is traveling along a

straight line at a constant speed of 800. meters

per second. The magnitude of the net force on

the space vehicle is

(1) 0 N (3) 8.00 * 10^2 N

(2) 1.60 * 10^2 N (4) 1.28 * 10^5 N

If the object is moving in a straight line at a constant speed, then that's

the definition of zero acceleration. It can only happen when the sum of

all forces (the 'net' force) on the object is zero.

And it doesn't matter what the object's mass is. That argument is true

for specks of dust, battleships, rocks, stars, rock-stars, planets, and

everything in between.