Angular motion problem (wheels on a car coming to a stop)

AI Thread Summary
The problem involves a car decelerating from 12.0 m/s to a stop with a constant deceleration of 1.90 m/s². The calculated stopping distance is 37.89 meters, leading to an initial conversion of that distance into radians and then revolutions based on the tire's radius of 0.40 m. The initial calculation yielded approximately 15.076 revolutions, but the answer was marked incorrect. A suggestion was made to verify the number of decimal places entered, as the method used to calculate revolutions based on distance and tire circumference was confirmed to be correct.
xregina12
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The driver of a car traveling at 12.0 m/s applies the brakes and undergoes a constnant decelertion of 1.90m/s^2.
How many revolutions does each tire make before the car comes to a stop assuming that the car does not skid and that the tires of radii of 0.40 m? answer in units of rev.

I used the equation Vf^2=Vi^2+2ad
0=144+2(-1.90)(d)
d=37.89meters
d=r(θ)
θ=37.89/0.40=94.725 radians
revolutions=94.725/(2pi)=15.076 revolutions.
However, I did not get a correct answer. Can anyone help? Did I do this the right way?
 
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You've worked out the distance it takes to stop correctly, but I don't follow your working after that. You know the radius of the tyre is 0.4m, so it's circumference = 2Pi*0.4=2.5137. The car stops in a distance of 37.89 meters, so the number of revolutions is just the distance it takes to stop divided by the circumference of the tyre. Hope that helps.
EDIT: Actually looking at that method I get the same answer as you, so I'm not sure why that's not the correct answer. If this is from an online homework site are you entering the correct number of decimals?
 
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