Mathematical and Physical Journal
for High Schools
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Problem P. 4507. (January 2013)

P. 4507. Two small balls are threaded to a horizontal frictionless rod which is attached to the wall. The heavy ball of mass M is moving towards the wall, and the other light ball of mass m (m\llM) is at rest at a distance of L measured from the wall. After the totally elastic collision, the light ball of mass m moves towards the wall and collides with it elastically. Then it moves towards the heavy ball and collides with it and the process is repeated. To what distance can the heavy ball approach the wall? (The two balls can be considered as pointlike objects.)

(6 pont)

Deadline expired on February 11, 2013.

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

Megoldásvázlat. \(\displaystyle L_\text{min}=L\sqrt{m/M}.\)


18 students sent a solution.
6 points:Novák László, Sal Kristóf, Szabó 928 Attila, Ürge László.
5 points:Antalicz Balázs, Balogh Menyhért, Csáky Pál, Kovács 444 Áron, Olexó Tünde, Sárvári Péter.
4 points:1 student.
3 points:1 student.
2 points:3 students.
1 point:2 students.
0 point:1 student.

Problems in Physics of KöMaL, January 2013