Power needed to keep car moving

  • Thread starter VanKwisH
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  • #1
VanKwisH
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Homework Statement


A 1200 kg car slows down from 90km/h to 70 km/h in about 5.0s on the level when it is in neutral. Approximately what power ( in watt's and hp ) is needed to keep the car travelling at a constant 80km/h?


Homework Equations


P = W / t


The Attempt at a Solution


I really have no idea ............ and
how much does 1hp = in watts and in joules ?
550 ft lbs/s = in joules and watts?
 

Answers and Replies

  • #2
rock.freak667
Homework Helper
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[tex]P=\frac{dW}{dt}=\frac{d}{dt}(Fs)=F\frac{ds}{dt}=Fv[/tex]


if you have the change in velocity and the time it acts for....you can find acceleration and F=ma...so you can find the power
 
  • #3
VanKwisH
108
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what does each of ur variables mean?? cause i think i use a different variables than u do and i find it confusing to understand
 
  • #4
rock.freak667
Homework Helper
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Oh well from the definition of power, the rate at which work,W, is done =[itex]\frac{dW}{dt}[/itex] since work done= Force(F)*distance(s) i.e.[itex]\frac{dW}{dt}=\frac{d}{dt}(Fs)[/itex] since force is constant you can then re-write it like [itex]\frac{d}{dt}(Fs)=F\frac{ds}{dt}[/itex] and well [itex]v=\frac{ds}{dt}[/itex]

In short: F=Force of car
P=power
v=velocity of car
 
  • #5
VanKwisH
108
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wha ??? so the answer is????
 

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