How Much Force to Move a 150 kg Crate on Different Friction Surfaces?

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Homework Help Overview

The discussion revolves around a physics problem involving a crate with a mass of 150 kg resting on a horizontal surface, examining the forces required to move it given different coefficients of friction. Participants explore the implications of static and kinetic friction in determining the necessary force to initiate and maintain motion.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Problem interpretation

Approaches and Questions Raised

  • Participants discuss drawing free body diagrams, calculating normal and frictional forces, and comparing applied forces to frictional forces. Questions arise regarding the relationship between the applied force and the force of friction, as well as the conditions for motion.

Discussion Status

Some participants have made progress in understanding the problem, particularly in calculating forces and recognizing the need for a greater applied force to overcome static friction. There is ongoing exploration of the differences between static and kinetic friction, with some guidance provided on how to approach the calculations.

Contextual Notes

Participants are working within the constraints of the problem's parameters, including specific coefficients of friction and gravitational acceleration. There is an emphasis on understanding the conditions under which the crate will move or remain at rest.

bmandrade
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A crate of mass 150.0 kg lies at rest on a horizontal storage room floor. The
coefficient of static friction between the crate and the floor is 0.70, and the
coefficient of kinetic friction is 0.35. (You may assume g = 10.0 m/s2).

a) Suppose someone pulls on a horizontal rope attached to the crate. They slowly
increase the tension in the rope. Draw a free body diagram of the system.

b) Suppose someone pulls on a horizontal rope attached to the crate with a force of
200 N. Does the crate remain at rest or start moving? If it moves does it have
constant speed or continue to accelerate? If it accelerates, what is its acceleration?
Under these conditions what is the frictional force on the crate?

c) Answer part (b) again if the pull on the rope is 1000 N.

d) What force on the rope is needed to start the crate sliding?
 
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What part are you having trouble with?
 
well i got part A now I am stuck on part B
 
Well, your going to have to see if the force of friction is less than or greater than the force that is being applied.
 
ok i got that normal force is 1500 and then i multiplied that times the coefficient which is .7 which gave me 1050 but then I am not sure is I am suppose to subtract that from the 200N which is the force from the rope also i don't know how to do what you just ask
 
Well basically you just look at what you have. You are pulling the crate at 200N while the force of friction is 1050. So is 200N greater than 1050N. No, so that box ain't going nowhere.
 
oh so in order to move the box you will need a force greater than 1050 right?
 
Yes sir. You need to make sure you understand the difference between kinetic friction and static friction. You need more force to get it moving then to keep it moving. Since the block is at rest you are correct in using the coefficient of static friction in your equation.

You showed that you didn't have enough force to overcome the force of friction, however, had the block already been moving then you would have used the coefficient of kinetic friction and therefore would have (in the part c) had enough force to move the block.
 
All makes sense now, Thank you so much!
 
  • #10
Your welcome
 

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