Assume the brakes of an automobile produce a constant deceleration of k ft/sec^2. Determine what k must be to bring an automobile traveling 60 mph to a rest in a distance of 100 ft from the point where breaks are applied?

Question

With the same k, how far would a car traveling 30mph travel before being brought to a stop?

Answer 1

60mph = 88ft/s, so you want k where
88-kt=0 so t = 88/k

88t-1/2 kt^2 = 100
88(88/k) - 1/2 k (88/k)^2 = 100
k = 38.72 ft/s^2

now you can solve the other part.