1. The problem statement, all variables and given/known data http://postimage.org/] [/PLAIN] [Broken] free picture upload 2. Relevant equations 3. The attempt at a solution I consider that if the fan is swinging, the source of sound (fan) will have an speed that lead to doppler's shift. but i can't calculate for this. i think speed of source will be ωR cos (ωt) (R is the radius of fan's swinging) but there is no data of R . I only know that in question 3 will answer nearly constant with time becuse source of sound will be a spot and we neglet the speed from swinging.