Calculating Work Done by Brakes

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Homework Help Overview

The problem involves calculating the work done by the brakes of a car as it slows down from an initial speed to a final speed. The context includes the mass of the car and the speeds in both kilometers per hour and meters per second.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • Participants discuss using conservation of energy as a potential approach. There is uncertainty about the provided answer and its units, with some expressing confusion over how to derive the answer.

Discussion Status

The discussion is ongoing, with participants sharing their attempts and expressing frustration over the lack of clarity on how to proceed. Some have noted the need for a reference point to begin their calculations.

Contextual Notes

Participants mention the absence of a friction coefficient and the challenge of working without complete information. There is also a reference to the lecturer's provided answer, which raises questions about its validity and derivation.

Chica1975
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Homework Statement



the driver of a car mass 1368kg braked momentarily to slow down from 92km/h (25.556m/s) to 63 km/h (17.5m/s) how much work was done by the brakes (friction).

Homework Equations


w = Fd
F=ma
difference between initial acceleration and final acceleration s 8.056m/s (25.556 - 17.5)
mg = 13406.40



The Attempt at a Solution



I ave drawn the picture, I have tried a number of calculations - I am completely lost - I have no friction coefficient and don't know where to start. I have looked a book I have that has problems but has nothing like this. Apparently, the answer is 237.
 
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Try to use conservation of energy. I have no idea where 237 comes from, it's much to low (and has no units!)
 
Thanks - this is the answer the lecturer has given for this question. I have no idea how to get it out.
 
the units are KJ
 
Thanks I tried to use conservation energy equation. I can't get this out.

Please can some explain to me step by step how to do this - I have been on this question for the last hour and a half and have tried all sorts of things with different equations - its not working.

I need a reference point to start from I have no idea - I am stuck.
 

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