need algebra word problem help

Algebra
Tutor: None Selected Time limit: 1 Day

the stopping distance D of a particular car after the brakes are applied varies directly as the square of the speed R. If the car is traveling 60mph it can stop in 200ft. how fast can the car go and still stop in 80ft?

Aug 30th, 2015

Thank you for the opportunity to help you with your question!

D=kR^2

so what is the constant k

D=200ft, R=60mph

k=D/R^2

k=200/(60*60)

k=200/3600

k=1/18

so lets find R when D is 80ft

 80=1/18*R^2

R^2=80*18/1

R^2=1440

R=square-root of 1440

R=37.9473319mph or 37.95(2dp)


Please let me know if you need any clarification. I'm always happy to answer your questions.
Aug 30th, 2015

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