# Problem P. 4361. (September 2011)

**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 pont)

**Deadline expired on October 10, 2011.**

Sorry, the solution is available only in Hungarian. Google translation

**Megoldás.** \(\displaystyle a)\) 54 km/h.

\(\displaystyle b)\) 1 s és 1,2 s.

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

### Statistics:

367 students sent a solution. 4 points: 281 students. 3 points: 47 students. 2 points: 15 students. 1 point: 12 students. 0 point: 10 students. Unfair, not evaluated: 2 solutions.

Problems in Physics of KöMaL, September 2011