Mathematical and Physical Journal
for High Schools
Issued by the MATFUND Foundation
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Problem P. 4726. (April 2015)

P. 4726. A narrow circular sector of a black disc is painted white. The disc is rotated about an axis which goes through its centre, and is perpendicular to the disc, and the rotated disc is illuminated with strobe light (a periodically flashing light source). What is the relationship between the number of revolutions $\displaystyle n$ of the disc and the flashing frequency $\displaystyle f$, if not only one, but a number of $\displaystyle p$ seemingly steady white sectors can be observed on the disc ($\displaystyle p=2, 3, 4, \ldots$)?

(4 pont)

Deadline expired on May 11, 2015.

Statistics:

 21 students sent a solution. 4 points: Szántó Benedek, Trócsányi Péter. 3 points: Berta Dénes, Fekete Panna, Gyöngyössy Natabara, Marosvári Kristóf, Nagy 555 Botond, Pszota Máté, Simon Dániel Gábor, Szépfalvi Bálint, Tanner Martin, Zöllner András. 2 points: 5 students. 1 point: 4 students.

Problems in Physics of KöMaL, April 2015