Final answer:
The tension in each of the two ropes holding up a motionless swing with a person weighing 400 N is 200 N. This assumes that the ropes are equally tensioned and vertical.
Step-by-step explanation:
When a person is sitting motionless on a swing, the net force in the vertical direction must be zero because there is no acceleration (according to Newton's first law of motion). Therefore, the force of gravity pulling down on the person (their weight) is balanced by the tension forces in the ropes holding up the swing. In this scenario, the weight of the person is 400 N and there are two ropes supporting the swing. If we assume the ropes have equal tension and that the swing is symmetrical, the tension in each rope will be half of the total weight.
To find the tension in each rope, you would divide the total weight by two: 400 N / 2 = 200 N in each rope. Hence, the correct answer is b. 200 N in each rope. This assumes that the ropes are vertical and the swing is not moving.