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Question:

A string 2.0m long and fixed at its ends is driven by a 240 Hz vibrator. The string vibrates in its third harmonic mode. The speed of the wave and its fundamental frequency is?

320m/s,120Hz

320m/s,80Hz

180m/s,80Hz

180m/s,120Hz

Solution:

Correct option is D. 320m/s, 80Hz
3(v/2L) = 240
3v/(22) = 240
v = 320m/s
Fundamental frequency = v/2L = 320/(22) = 80Hz