Kinetic frictional force Definition and 14 Threads

Reading again this Insight, I have a question regarding "I. Work done against friction" section. In that problem (billiard ball of radius ##R## initially spinning in the air then falling on a pool table) the system under analysis is "billiard ball". The work-energy theorem (which would be...

Hey all, I was recently searching for kinetic friction coefficients, and I noticed that for a reason which is unknown to me, some materials had not been appointed such coefficient. The specific kinetic friction coefficient that I'm looking for is aluminum on greasy/lubricated cast iron. Any type...

Homework Statement The speed of a 4.0-N hockey puck, sliding across a level ice surface, decreases at the rate of 0.61 m/s2. The coefficient of kinetic friction between the puck and ice is: A) 0.062 B) 0.25 C) 0.41 D) 0.62 E) 1.2 Homework Equations I'm not too sure but i know that : If the...

Could anybody explain what happens at the molecular level when one of the two bodies in a contact starts moving w.r.t other, i mean in this process what causes kinetics friction force, i tried myself to think of it but i could not come up with any, so please help me.

Homework Statement A child is playing with their Hot Wheel cars. They have set up a track which is initially horizontal but then ascends to a second horizontal section which is 50 cm higher than the initial track. The track is friction-less until the car reaches the upper section of the track...

The alarm at a fire station rings and a 71.3-kg fireman, starting from rest, slides down a pole to the floor below (a distance of 3.63 m). Just before landing, his speed is 1.42 m/s. What is the magnitude of the kinetic frictional force exerted on the fireman as he slides down the pole? Givens...

Homework Statement Using the relation ## tan \theta = \mu_k ## what angle should the rope make with the horizontal in order to minimize the work done per unit distance traveled along the ground. Homework Equations ## W = Fdcos\phi ## The Attempt at a Solution I found...

Homework Statement I have a few questions I need help with on my assignment. I cannot wrap my head around this work and energy chapter. Anyway here it is; A 62.7-kg skier coasts up a snow-covered hill that makes an angle of 25.2° with the horizontal. The initial speed of the skier is...

Homework Statement A 64.9-kg skier coasts up a snow-covered hill that makes an angle of 23.4 ° with the horizontal. The initial speed of the skier is 8.95 m/s. After coasting a distance of 2.31 m up the slope, the speed of the skier is 4.40 m/s. (a) Find the work done by the kinetic frictional...

The alarm at a fire station rings and a 96.0-kg fireman, starting from rest, slides down a pole to the floor below (a distance of 3.55 m). Just before landing, his speed is 1.79 m/s. What is the magnitude of the kinetic frictional force exerted on the fireman as he slides down the pole...

Homework Statement Answer Chapter 6, Problem 73 Cutnell & Johnson 7th edition A 356 N force is pulling an 90.2-kg refrigerator across a horizontal surface. The force acts at an angle of 25.6 ° above the surface. The coefficient of kinetic friction is 0.258, and the refrigerator moves...

Hi there, I'm doing a problem in my book ("Check your understanding" 4.3 in Cutnell/Johnson, 7th ed.). The book says the answer is x=43 degrees, but I don't know how to find it exactly. Given that it's an in-chapter problem, I'm guessing there's something wrong with my brain, but I'd...

A 300N force is pulling an 90.0 kg refrigerator across a horizontal surface. The force acts at an angle of 22.0° above the surface. The coefficient of kinetic friction is 0.200, and the refrigerator moves a distance of 6.00 m. i found out the work done by pulling force is 1669 J and its...

Why is the kinetic frictional force always less than the static? One other question, when a car moves along a curved road, the direction of the static frictional force is toward the center. But we were told, since the elemantary school, that the frictional force is always at the opposite...