**P. 4361.** A car travelled at a speed of , when a pedestrian stepped down from the sidewalk. The driver braked suddenly and the accident was avoided. The braking-distance was 6.25 m.

*a*) The car in the next lane could only stop in a distance of 9 m. What was the speed of this car if the accelerations of the two cars were the same.

*b*) What were the braking times of the two cars? *c*) What is the ratio of their initial kinetic energies if their mass is the same?

(4 points)

**Deadline expired on 10 October 2011.**

\(\displaystyle b)\) 1 s és 1,2 s.

\(\displaystyle c)\) A mozgási energiák aránya 1,44.