a student stands several meters in front of a smooth reflecting wall, holding a board on which a wire is fixed at each end. the wire, vibrating in...

a student stands several meters in front of a smooth reflecting wall, holding a board on which a wire is fixed at each end. the wire, vibrating in its third harmonic, is 75 cm long, has a mass of 2.25g, and is under a tension of 400N. A second student, moving toward the wall, hears 8.3 beats per second. What is the speed of the student approaching the wall?