Final answer:
The force the floor exerts on each leg vertically upward when the magnitude is 100 N is the normal force. It's equal to the object's weight and directed upward, counteracting the force of gravity. The correct equation reflecting this force is N= mg, where g is the acceleration due to gravity.
Step-by-step explanation:
The force that the floor exerts on each leg vertically upward when the magnitude is 100 N is the normal force. The normal force is a contact force exerted by a surface against an object that is pressing against it.
In this case, because the object is at rest and not accelerating vertically, the normal force is equal in magnitude and opposite in direction to the gravitational force acting on the object, ensuring the net force in the vertical direction is zero. Consequently, the normal force equals the weight of the object and is directed upward.
When an object with mass m is at rest on a floor, the normal force N is equal to mg, where g is the acceleration due to gravity, and points in the upward direction to counteract the downward force of gravity. The equation N = mg reflects this relationship between the normal force, mass, and gravity. Therefore, option B) N= mg in upward direction is the correct representation of the normal force in the context of the student's question.