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The alarm at a fire station rings and an 86-kg fireman, starting from rest, slides down a pole to the floor below (a distance of 4.0 m). Just before landing, his speed is 1.4 m/s. What is the magnitude of the kinetic frictional force exerted on the fireman as he slides down the pole?

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820 $\mathrm{N}$

Physics 101 Mechanics

Chapter 4

Forces and Newton’s Laws of Motion

Newton's Laws of Motion

Applying Newton's Laws

Rutgers, The State University of New Jersey

University of Washington

Hope College

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.

03:43

In physics, dynamics is the branch of physics concerned with the study of forces and their effect on matter, commonly in the context of motion. In everyday usage, "dynamics" usually refers to a set of laws that describe the motion of bodies under the action of a system of forces. The motion of a body is described by its position and its velocity as the time value varies. The science of dynamics can be subdivided into, Dynamics of a rigid body, which deals with the motion of a rigid body in the frame of reference where it is considered to be a rigid body. Dynamics of a continuum, which deals with the motion of a continuous system, in the frame of reference where the system is considered to be a continuum.

03:49

The alarm at a fire statio…

05:00

03:31

The alarm at a fi re stati…

01:24

Starting from rest, a 93-k…

01:16

A fireman has mass $m$; he…

02:35

A 80.0 -kg fireman slides …

01:33

03:01

A 70 kg firefighter slides…

06:16

An 80 -kg fireman slides 5…

14:06

Down the Pole. A fireman o…

09:48

we begin this question by calculating the acceleration off the fire man. We can do that by using. Torricelli's equation tells us that the final velocity squared is interested. Initial velocity squared plus two times his acceleration times. He's displacement. Also, let me choose that everything that is pointing upwards is positive. Then his final velocity is 1.4 meters per second, his initial velocity zero because he starts from rest, then we have plus two times the acceleration times they displacement on displacement Waas four meters but four meters downwards. Therefore, he started at some height and finishes at his water height, meaning that in my reference frame the displacement is negative and equals two minus four liters. Then we solve this equation for eight as follows. 1.4 squared is the goes to minus eight times a so that his acceleration is equals to 1.4 squared, divided by eight with a minus sign in front of it on. These is minus 0.245 meters per second squared. Now that you know his acceleration, we can use Newton's second law to calculate what is the frictional force. Newton's second law tells us that the net force is the cost of the mass times acceleration off the fireman. Then the net force is composed by true forces, the frictional force that points of ports. So it's positive minus the weight force that points downwards under four negative. And these Zico's to the Mass 86 kilograms times acceleration off minus zero point True for five meters per second squared. Then the frictional force is he goes to 86 times, minus 0.2 for five. Plus he's wait. Remember that the weight is given by the mass times acceleration off gravity, which is approximately 9.8 meters per second, squared near the surface of the earth. So plus 86 times 9.8 then the frictional force is approximately 820 new tons.

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