It is (b. unbalanced force), because they person who is pulling 600 newtons is pulling harder than the person pulling with 500. This causes the unbalance force of 100 newtons.
If two people are pulling against each other with forces of 500 Newtons and 600 Newtons respectively, there exists an unbalanced force. The difference in forces (100 Newtons in this case) will cause a net motion in the direction of the larger force, according to Newton's Second Law of Motion. Moreover, according to Newton's Third Law of Motion, while the forces two objects exert on each other are equal in magnitude and opposite in direction, an unbalanced force results when the sum of forces on an object is not zero, leading to a change in the object's motion.
For a person standing on a scale, the type of force pulling them down is gravitational force, and the force provided by the scale to hold them up is the normal force, which is equal in magnitude and opposite in direction to the gravitational force. This can be depicted in a free body diagram, with the gravitational force pointing downwards and the normal force pointing upwards.
The answer to the question is B. Unbalanced force, because the forces of 500 Newtons and 600 Newtons are not equal. This results in a net force of 100 Newtons acting in the direction of the stronger force.
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