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P. 3798. A 0.8 m long rod joins to a vertical axle with a bearing at its middle. The rod has negligible mass and it is frictionless. We thread point-like pierced balls of masses of 200 g on both of its ends. The two balls positioned symmetrically on both sides of the axis are linked with a thin thread of a length of 0.2 m. At the ends of the rod there are non-elastic bumpers. We spin this system with an angular velocity of 2 s-1 and then we burn the thread.

a) What path do the balls follow?

b) How much does the rod turn in 1 s after burning the fibre.

c) In what time does the rod turn by an angle of 180o?

d) What distance is done by the balls during the half turn of the rod?

e) What percentage is the mechanical loss?

(5 points)

Deadline expired on 11 May 2005.

Statistics on problem P. 3798.
 36 students sent a solution. 5 points: Beck Zoltán, Domonkos Tamás, Dudás János, Farkas Ádám László, Filep Tamás, Gondán László, Gyenis András, Kónya 495 Gábor, Lantos Judit, Meszéna Balázs, Nagy 555 Zoltán, Nyíri Dávid Ákos, Pálinkás Csaba, Pálovics Róbert, Pósa László, Széchenyi Gábor, Szilágyi Zsombor, Szolnoki Lénárd, Takátsy Balázs. 4 points: Hagymási Imre, Pásztor 001 Attila, Szentandrási István, Szurmai Csongor, Tüzes Dániel, Werner Miklós. 3 points: 3 students. 2 points: 1 student. 1 point: 4 students. 0 point: 3 students.

• Problems in Physics of KöMaL, April 2005

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