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Chapter 4: Problem 37

Margie, who weighs \(543 \mathrm{N},\) is standing on a bathroom scale that weighs \(45 \mathrm{N}\). (a) With what force does the scale push up on Margie? (b) What is the interaction partner of that force? (c) With what force does the Earth push up on the scale? (d) Identify the interaction partner of that force.

Short Answer

Expert verified
(b) What is the interaction partner of the force in part (a)? (c) What is the force with which the Earth pushes up on the scale? (d) What is the interaction partner of the force in part (c)? Answer: (a) The force the scale pushes up on Margie is 543 N. (b) The interaction partner of the force in part (a) is Margie herself, exerting a force of 543 N downward. (c) The force with which the Earth pushes up on the scale is 588 N. (d) The interaction partner of the force in part (c) is the bathroom scale itself, exerting a force of 588 N downward.

Step by step solution

01

Determine the force the scale pushes up on Margie

According to Newton's third law, for every force, there's an equal but opposite force. The scale pushes up on Margie with a force equal to her weight acting downward. Therefore, the force the scale pushes up on Margie is simply 543 N.
02

Identify the interaction partner of the force in part (a)

The interaction partner of the force on Margie is the force with which Margie pushes down on the scale. This force is equal (magnitude) and opposite (direction) to the force the scale exerts on Margie. So, the interaction partner of the force exerted on Margie is Margie herself and the force is 543 N, downward.
03

Determine the force with which the Earth pushes up on the scale

There are two forces acting on the scale: the force with which Margie pushes down on the scale and the force due to the weight of the scale. The force on the scale is the sum of these two forces: Force on scale = Force due to Margie + Force due to scale Force on scale = 543 N (Margie's force, downward) + 45 N (Scale's force, downward) To achieve equilibrium (i.e., not accelerate), the Earth should exert an equal, upward force on the scale. Therefore, the Earth pushes up on the scale with a force of (543 N + 45 N) = 588 N.
04

Identify the interaction partner of the force in part (c)

The force with which the Earth pushes up on the scale has an interaction partner that is equal in magnitude and opposite in direction. The interaction partner of this force would be the force with which the scale pushes down on the Earth (-588 N). The interaction partner of the force exerted by Earth on the scale is the bathroom scale itself, and the force acts downward with a magnitude of 588 N.

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