Brake System (Torque and Friction)

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Homework Help Overview

The problem involves a car's brake system, focusing on the relationship between torque, friction, and the forces required to slow the vehicle effectively. The car's specifications, including mass, tire diameter, and coefficients of friction, are provided to explore the necessary calculations for braking force.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the appropriate values to use for calculations, particularly questioning which friction coefficient—static or kinetic—should be applied in the context of the problem. There is also consideration of the role of the wheel's radius in the calculations.

Discussion Status

The discussion is ongoing, with participants providing hints and engaging in questioning to clarify the concepts involved. Some guidance has been offered regarding the use of friction coefficients, but no consensus has been reached on the correct approach to the problem.

Contextual Notes

Participants are navigating the complexities of the problem, including the presence of multiple friction forces and the implications of relative motion in the braking scenario. There is uncertainty regarding the application of static versus kinetic friction in the calculations.

zewei1988
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Homework Statement


The tires of a 1500 kg car are 0.600 m in diameter and the coefficients of friction with the road surface are µs = 0.800 and µk = 0.600. Suppose the car has a disk brake system. Each wheel is slowed by the frictional force between a single brake pad and the disk-shaped rotor. On this particular car, the brake pad comes into contact with the rotor at an average distance of 18.5 cm from the axis. The coefficients of friction between the brake pad and the disk are µs = 0.588 and µk = 0.490. Calculate the normal force that must be applied to the rotor such that the car slows as quickly as possible.


Homework Equations


Torque = Fd
Friction = n* coefficiant


The Attempt at a Solution


I'm not very sure which values to use. All I did was find the torque required and find the amount of force to apply

0.8 * 1500/4 * 9.8 = 0.185 * F * 0.588

8.11, 1.35 and 7.30 kN are some of the answers that I submitted and are all wrong.
 
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Hi zewei1988! :smile:

Hint: you haven't used the radius of the wheel. :wink:
 
But which friction coefficient should I use? Static or Kinetic?
 
Which do you think? And why? :smile:
 
kinetic? cos it's moving?
 
That's the general idea! :smile:

But there are two friction forces here … is there relative motion in both cases? :wink:
 
I dun really know.
 

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