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You leave the doctor's office after your annual checkup and recall that you weighed 683 $\mathrm{N}$ in her office. You then get into an elevator that, conveniently, has a scale. Find the magnitude and direction of the elevator's acceleration if the scale reads (a) $725 \mathrm{N},(\mathrm{b}) 595 \mathrm{N}$

See explanstion for result.

Physics 101 Mechanics

Chapter 4

Newton's Laws of Motion

Physics Basics

Motion Along a Straight Line

Motion in 2d or 3d

Rutgers, The State University of New Jersey

University of Michigan - Ann Arbor

University of Sheffield

McMaster University

Lectures

03:28

Newton's Laws of Motion are three physical laws that, laid the foundation for classical mechanics. They describe the relationship between a body and the forces acting upon it, and its motion in response to those forces. These three laws have been expressed in several ways, over nearly three centuries, and can be summarised as follows: In his 1687 "Philosophiæ Naturalis Principia Mathematica" ("Mathematical Principles of Natural Philosophy"), Isaac Newton set out three laws of motion. The first law defines the force F, the second law defines the mass m, and the third law defines the acceleration a. The first law states that if the net force acting upon a body is zero, its velocity will not change; the second law states that the acceleration of a body is proportional to the net force acting upon it, and the third law states that for every action there is an equal and opposite reaction.

04:16

In mathematics, a proof is a sequence of statements given to explain how a conclusion is derived from premises known or assumed to be true. The proof attempts to demonstrate that the conclusion is a logical consequence of the premises, and is one of the most important goals of mathematics.

04:58

After an annual checkup, y…

07:04

04:45

You leave the doctor'…

04:35

A person stands on a scale…

02:43

01:43

A $75-\mathrm{kg}$ man sta…

04:41

You walk into an elevator,…

09:34

05:20

A 700 -N man stands on a s…

So here you have the the force of gravity or w wait, act downwards and then end the normal force acting upwards. Ah, it's a force. The scale exerts on you. And the convention we choose to work with is that upward direction is positive. Downward direction is negative. And so ah, very simply, we use Newton's second law states that the sum of forces in any direction and so this would be vertical are y direction which is equal to mass times acceleration in that direction. No film in both these cases we have that and minus w equals m times the acceleration, acceleration being the thing that we don't know. Um, so so you have that acceleration is and minus w Now put Forrest minus the way over your mass. Okay, so first thing you do is fine. Glass and Mass is simply found from w equals and she and so you know, W which he has six, 183 Newtons over G uh, which is 9.8 meters per second squared or the earth. And so you get 9 69.7 kilograms for your mass. You know that you have mass you ready to five acceleration Both cases. First case and is 7 25 w again is 63. They're both meetings. You divide that by the mass, which is 69.7 kilograms. And so this will give you something in units of meters per second squared and it turns onto me point 603 meters per seconds. Quick. And so this is a positive value, right? Positive. And so, by our convention, positive is upward. So acceleration is upwards. In this case, in part B, all that's different is that the normal force this time it's 5 95 way is the same. 6 83 and a mass, of course, is still the same. 69.7 Kill O's And so that gives your negative 1.26 meters per second squared. Okay. And this means that this acceleration is acting downwards. Meyer convention. So acceleration is acting downwards and that's it

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