A driver in a car traveling at a speed of 60 mi/h sees a deer 100 m away on the road. Calculate the minimum constant acceleration that is necessary for the car to stop without hitting the deer (assuming that the deer does no move in the meantime).

Question

Work (so far):
100 m x 1 km/1000 m x .621 mi/km =0.0621 mi

Answer (back of the book): -3.60 m/s^2

Answer 1

60 mph = 88 ft/s = 26.82 m/s
To decelerate from 26.82 m/s to 0 in 100 m, the time of travel will be
(100 m)/(average speed) = 100/13.41= 7.46 s. The deceleration rate is 26.82 m/s/7.46 s = -3.59 m/s^2
Since there are only two significand figures ikn this problem, it should be rounded to -3.60 m/s^2.