Mathematical and Physical Journal
for High Schools
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Problem P. 4361. (September 2011)

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 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.


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