Oct 12, 2011
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A car is moving at 40mph. If the mass of the car is 2,300 kg and the coefficient of kinetic friction is 0.4, what is the stopping distance in ft?
 

BerkReviewTeach

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First convert 40mph to m/s
KE = Fn * d
1/2 mv^2 = 0.4mg * d
(v^2)/(2 *0.4*g) = d (in meters, so multiply by 3 to get ft)

is the answer ~120 ft?
Spot on solution, although I came up with a slightly larger final number (in the 140 m +/- range). It comes down to our rounding differences I suspect. In a multiple choice scenario, all three answers so far will likely lead to the best answer of the four choices.
 
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