Waves

Paragraph for next two questions
S1 and S2 are two identical sound sources of frequency 656‌Hz. The source S1 is located at O and S2 moves anticlockwise with a uniform speed 4√2ms−1 on a circular path around O, as shown in the figure. There are three points P,Q and R on this path such that P and R are diametrically opposite while Q is equidistant from them. A sound detector is placed at point P. The source S1 can move along direction OP.
[Given: The speed of sound in air is 324m s−1 ]