Wave Motion And Sound Problems - Physics 11th - Chapter 8 - Sindh Textbook Board (stb problems)

 

WAVE MOTION AND SOUND

(PROBLEMS)

Problem 8.1. An object is connected to one end of a horizontal spring whose other end is fixed. The object is pulled to the right (in the positive x-direction) by an externally applied force of magnitude 20 N causing the spring to stretch through a displacement of 1 cm (a) Determine the value of force constant if, the mass of the object is 4 kg (b) Determine the period of oscillation when the applied force is suddenly removed.

Problem 8.2. A body hanging from a spring is set into motion and the period of oscillation is found to be 0.50 s. After the body has come to rest, it is removed. How much shorter will the spring be when it comes to rest?

Problem 8.3. A pipe has a length of 2.46 m. (a) Determine the frequencies of the fundamental mode and the first two overtones if the pipe is open at both ends. Take v = 344 m/s as the speed of sound in air. (b) What are the frequencies determined in (a) if the pipe is closed at one end? (c) For the case of open pipe, how many harmonics are present in the normal human being hearing range (20 to 20000 Hz)?

Problem 8.4. A standing wave is established in a 120 cm long string fixed at both ends. The string vibrates in four segments when driven at 120 Hz (a) Determine the wavelength (b) What is the fundamental frequency?

Problem 8.5. Calculate the speed of sound in air at atmospheric pressure P = 1.01 x 10°N/m?, taking λ = 1.40 and p = 1.2kg/m3.

Problem 8.6. A sound wave propagating in air has a frequency of 4000 Hz. Calculate the percent change in wavelength when the wavefront, initially in a region where T = 27°C, enters a region where the air temperature decreases to 10°C.

Problem 8.7. The frequency of the second harmonic of an open pipe (open at both ends) is equal to the frequency of the second harmonic of a closed pipe (open at one end). (a) Find the ratio of the length of the closed pipe to the length of the open pipe.(b) If the fundamental frequency of the open pipe is 256 Hz, what is the length of pipe? (Use v = 340 m/s).

Problem 8.8. A 256 Hz tuning fork produces four beats per second when sounded with another fork of unknown frequency. What are two possible values for the unknown frequency?

Problem 8.9. An ambulance travels down a highway at a speed of 75 mi/h. Its siren emits sound at a frequency heard by a person in a car traveling at 55 mi/h in the opposite direction as the car approaches the ambulance and as the car moves away from the ambulance.

Problem 8.10. A car has siren sounding a 2 kHz tone. What frequency will be detected as stationary observer as the car approaches him at 80 km/h? Speed of sound = 1200 km/h.