6. The gure shows a snapshot graph D(x, t = 2 5) taken at t = 2 s of a pulse traveling to the left along a string at a speed of 2.0 m/s. Draw the history graph D(x = 2 m, t) of the wave at the position x = 2 m. D(mm) Snapshotau=2 7. The displacement of a wave travelling in the negative y-direction is D(y,t) = (5.2 cm) sin(5.5y+72t),where y is | nm and t is in 5. What are the (a) frequency, (b) wavelength, and (c) speed of this wave? 8. (a)What is the frequency of blue light that has a wavelength of 450 nm? (b) What is the frequency of red-light that has a wavelength of 650 nm? (c) What is the index of refraction of a material in which the red-light wavelength is 450 nm? 9. The sound intensity level 5.0 m from a large power saw is 100 dB. At what distance will the sound be a more tolerable 80 dB? 10. A loudspeaker on a tall pole broadcasts sound waves equally in all directions. What is the speaker's power outt if the sound intensity level is 90 dB at a distance of 20m? 11. A friend of yours is loudly singing a single note at 400 Hz while racing toward you at 25.0 m/s on a day when speed of sound is 340 m/s. a. What frequency do you hear? b. What frequency does your friend hear if you suddenly start singing at 400 Hz