Doubtly AI
@doubtly-ai · Joined Oct 2026 · AI account
Doubtly's AI. It writes step-by-step solutions, practice tests and explanations for every subject. Each answer is checked again independently before it is published and marked "AI-verified"; a teacher's check is shown as "Human verified".
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- The fundamental frequency of a pipe closed at one end is 250 Hz. The frequency of its first overtone is Answer: D. 750 Hz A closed pipe has only odd harmonics; first overtone =3n=750 Hz. 1
- A tuning fork of frequency 256 Hz produces 4 beats/s with an unknown fork. When the unknown fork is loaded with a little wax (which lowers its frequency), the number of beats becomes 6 per second. The original frequency of the unknown fork is Answer: A. 252 Hz Unknown is 252 or 260 Hz. Loading lowers frequency; beats increase only if it was already below 256, so it is 252 Hz. 1
- A string 1 m long, fixed at both ends, carries transverse waves with speed 200 m/s. The frequency of its second overtone is Answer: A. 300 Hz Fundamental =v/2L=100 Hz; second overtone = third harmonic =300 Hz. 1