A car is traveling on a level road with speed vo at the instant when the brakes

Question

A car is traveling on a level road with speed vo at the instant when the brakes lock, so that the tires slide rather than roll. Use the work energy theorem to calculate the minimum stopping distance of the car in terms of u. g, and the coefficient o kinetic between the tires and the road iction A You may want to review (Pages 177 182) For related problem-solving tips and strategies, you may want to view a Video Tutor Solution of Using work and energy to calculate speed Submit Request Answer Part B By what factor would the minimum stopping distance change if the coefficient of kinetic friction were doubled? Sa

Explanation / Answer

(a) friction force, fk = uk N = uk m g

Applying work - energy theorem,

Net work done = change in KE

- f.d = m vf^2 / 2 - m vi^2 /2

- uk m g d = 0 - m v0^2 /2

d = v0^2 / (2 uk g)

(B) uk' = 2 uk

then d' = d/2

Ans: 0.5

(C) v0' = 2 v0

d' = 2^2 d = 4 d

Ans: 4

(D) v0' = 2 v0 and uk' = 2uk

d' = 2^2 / 2 d

d' = 2 d

Ans: 2

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