Can the KE of a car be converted into work by stopping it at 100 km/hr?

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Homework Help Overview

The discussion revolves around calculating the work required to stop a car with a mass of 1000 kg traveling at a speed of 100 km/hr, focusing on the relationship between kinetic energy and work.

Discussion Character

  • Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to apply the kinetic energy formula but encounters issues with unit conversion from km/hr to m/s. Some participants question the setup of the conversion process and offer guidance on the correct conversion factors.

Discussion Status

Participants are actively discussing the conversion of units and the application of the kinetic energy formula. There is a recognition of a potential mistake in the conversion process, and some guidance has been provided regarding the correct factors to use.

Contextual Notes

The original poster expresses uncertainty about their calculations and mentions a discrepancy between their results and the answer provided in a textbook. There is an indication that the discussion is constrained by the need for accurate unit conversion.

rueberry
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How much work is required to stop a 1000 kg car traveling at 100 km/hr?

What I was thinking was that I would use the formula for KE,
KE=1/2mv2 (last two of course is for squared
since the KE would equal work. I have gotten as far as:

KE= 1/2(1000 kg)(100km/hr)2

I am assuming that somewhere there is a conversion needed, I'm just not getting the next steps.
 
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Which next steps? Just convert the km/hr into m/s and you're done.
 
Then maybe I'm not setting up the conversion correctly, I was using dimensional analysis and set it up

(100 km/hr) (1000m) (3600 sec) = 3.6 x 10^8
(1 km) (1 hr)

but I know this is wrong, by the time you square it and finish the equation, its way too big. The answer in the book is 386,000J, but I keep getting answers with 360 b/c of the sec. I'm sure this is a simple mistake I'm making, but I'm still stuck. Sorry.
 
the hour is on the bottom!
your conversion factors should be
(1000 m)/(1 km) * (1 hr)/(3600 s)

I suppose here, 100% of the Work removes KE.
 

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