Question

A person standing on a weighing scale sees a reading on the scale as $148$ pounds. This person is acted on by
$(A)$ No forces at all
$(B)$Only one force, of $296$ pounds
$(C)$Two forces of equal size acting in opposite directions
$(D)$Only one force of $148$ pounds, as shown by the reading on the scale

Answer 1

To solve this question you must be aware of the three laws of motion. After analyzing the three laws of motion, one will be able to decipher which one of the three laws is most applicable to the solution. Once you determine which law should be applied in this question, one can easily solve this question. Then compare the solution to the given options to determine which one is the correct answer.

Complete step by step answer:
So first let’s mention the three laws of motion. That is Newton’s law of motion. These laws give the relations between the forces that act on a body and the motion of the body.
First law: According to the first law, unless a force acts on a body at rest or motion moving with constant speed, these bodies will continue in the same state. That is the body will continue in the state of rest or a continuous state of motion unless a force is acted upon these bodies.
Second law: This law mentions that force acting on a body is equal to the rate of change in the momentum. As we are aware, momentum is equal to the product of mass and velocity.
Third law: According to this law, when two bodies interact, they apply forces that are equal in magnitude but in opposite directions.
Now that we know the three laws of mention, we can analyze which one of the three laws applies to the question.
Newton’s third law is the most suitable law to solve this question. It talks about forces acting on a body, which are equal in magnitude and opposite in direction.
The question mentions a person standing on the weighing scale. So from the third law, we know that two forces are acting on the object. Also, in addition, we know that these forces are equal in magnitude and that they are opposite in direction. So the third option is the correct answer for this question.
$(A)$This is the wrong option because forces are acting.
$(B)$This option is also wrong as two forces are interacting.
$(C)$ This option is correct as it talks about the two forces, that their magnitudes are equal and that they are acting in opposite directions.
$(D)$This option is wrong as there are two forces in interaction with each other.

So, the correct answer is “Option C”.

Note: To understand the third law better, consider a situation in which a table is placed on top of a table. In this case, we observe that the book applies a downward force that is equal in magnitude to its weight on the table. So as per the third law, the table also applies a force that is equal in magnitude and opposite in direction to the book. To prevent the book from deforming the table slightly, it pushes back the book by applying force that is equal in magnitude to the weight of the book.