A source of sonic oscillations with frequency \(v_{0}=1700 \mathrm{~Hz}\) and a receiver are located on the same normal to a wall. Both the source and the receiver are stationary, and the wall recedes from the source with velocity \(u=6.0 \mathrm{~cm} / \mathrm{s} .\) Find the beat frequency registered by the receiver. The velocity of sound is equal to'. \(v=340 \mathrm{~m} / \mathrm{s}\).