Suppose that the sound level of a conversation is initially at an angry 74 dB and then drops to a soothing 51 dB. Assuming that the frequency of the sound is 521 Hz, determine the (a) initial and (b) final sound intensities and the (c) initial and (d) final sound wave amplitudes. Assume the speed of sound is 344 m/s and the air density is 1.21 kg/m3.

Friction force is equal to the net force of the car.             fn                           |ff< ·                       |                     fgfg and fn cancel out.55 km/h is 15.2778 m/s. this is the initial velocityfinal velocity is 0 m/sfind acceleration using kinematic equationv² = v₀² + 2adsince v = 00 = v₀² + 2ada = -v₀²/(2d)a = -(15.2778 m/s)/(2 * 38m) a = -3.2418 m/s²find net force and you find friction.f = ma f = (1165 .2418 m/s²)f = 3776.7 n = ffw = ff · dw = (3776.7 n)(38 m)w = -1.4 × 10^5 jthe friction forces do 1.4 × 10^5 j of work on the car

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