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Work and Energy of a car

  • Thread starter rueberry
  • Start date
5
0
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.
 

Answers and Replies

quasar987
Science Advisor
Homework Helper
Gold Member
4,771
7
Which next steps? Just convert the km/hr into m/s and you're done.
 
5
0
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.
 
lightgrav
Homework Helper
1,248
30
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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