A driver is traveling on dry pavement at a high rate of speed when she spots a d

Question

A driver is traveling on dry pavement at a high rate of speed when she spots a deer in the road. She slams on her brakes and locks up the wheels, going into a skid, and manages to stop just before striking the deer. (a) If she was traveling 35 mph, how far away was the deer when she hit the brakes? (b) Repeat part (a) but with the assumption that the car had had antilock brakes that limit the wheel torque so that it is slightly below the skid threshold. For both (a) and (b) take s = 0:7 for the wheels/pavement, and k to be 0.4.

Explanation / Answer

35 mph = 15.55 m/s

a) For skidding kinetic friction is in effect

a = -ng = -0.4 x 9.8 = -3.92 m/s^2

using

V^2 = u^2 + 2as

0 = 15.55^2 -2 x 3.92 x s

s = 30.84 m

b)

For antilock brakes, static friction is in effect

similar calculations will give

s = 17.62m

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