18. Waves & Sound
Standing Waves
15PRACTICE PROBLEM
Consider an inextensible and massless string of length L suspended from the top of a roof. A block of mass mb is firmly attached to the string's lower end. When the string is wiggled, a third-harmonic standing wave of frequency 250 Hz is set up on the string. If an additional mass of 1.5 kg is added to the lower end, the third harmonic frequency is shifted to 285 Hz. Calculate the block's mass.
Consider an inextensible and massless string of length L suspended from the top of a roof. A block of mass mb is firmly attached to the string's lower end. When the string is wiggled, a third-harmonic standing wave of frequency 250 Hz is set up on the string. If an additional mass of 1.5 kg is added to the lower end, the third harmonic frequency is shifted to 285 Hz. Calculate the block's mass.