Answer to Question #70015 in Mechanics | Relativity for Anthony Gonzalez

Question

A person driving a car suddenly applies the brakes. The car takes 4 seconds to come to rest while traveling 20 meters at constant acceleration. Can the speed of the car immediately before the brakes were applied be determined without first determining the car's acceleration?

Answer 1

Yes. The speed of the car immediately before the brakes were applied is
v=at.
d=(at^2)/2→a=2d/t^2 .
v=2d/t^2 t=2d/t=2(20)/4=10 m/s.
Answer: 10 m/s.