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P. 4361. A car travelled at a speed of 45~\frac{\rm km}{\rm h}, 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.


Google Translation (Sorry, the solution is published in Hungarian only.)

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

\(\displaystyle b)\) 1 s és 1,2 s.

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


Statistics on problem P. 4361.
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

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