Question

An ambulance is moving with a velocity of 45.0 m/s. The siren has a frequency of 130 Hz. The temperature of the air outside is 90° F a) What frequencies are observed by a stationary person on the sidewalk as the ambulance approaches and after it passes? b) The ambulance now stops and you run towards it at 4.0 m/s along the sidewalk. What is the frequency you observe? c) The sound intensity level of the siren is 110 dB. What is the sound intensity of the siren? d) Calculate the amount of time required for 0.1 J of energy to transfer through an area of 0.0im

Answer 1

we coun Using, Doppler's formula Calculate the frequency observed by reseivel from moving to Dopplen's formula, source. f= e Iva CIVB ) to Vera - ve to = frequency of source velocity of recener treif receiver appraches towards source, if receiver runs away from source. Vsa velocity of source, tve if moving - ve if moving towards away from receiver receiver C = speed / velocity of wave. part (a) when Ambulance is abbraching f ( Cave ) to c-Vg CS Scanned with CamScanner

O vra Vs to = 130 H2 45 mis C- at T= 90°F velocity T: 40°F of sound 39.22° c C = 3313 + (0.6x1) mls c = 331.3 + 10.6 x 32.93) 350.63 a mis put all these value in above ean. fa (ved to 130 350.632 350.632 – 45 47 1.147 x 130 149.14 H2 After when Ambulance passes the receiver ( ctve ) to as, fa CAVs Ve=0 Vs= 45 m/s c = 350.632 mis fo=130 M2 fa léans)'3c 130 350.632 350.632 +45 ta 0.886 X 130 115.21 Hz f = 115:21 Hz CS Scanned with CamScanner

이 Wm2 NOW, B 1 o d3 A B (dB) lo | (품 lo 10910 -) 0 Ilo =) 1lo 10gio ( 프 의의 Toi -) - 11 AY 2,303 In (..) 1. (..) 1 x 2.3o3 11 x 9.30 3 T e 퓨 16-12 || X 9-303 (2) -) T = X e 112 x 1. oo S x ) 2 x 10 10~) w/m² sounds 50 intensity is ñ CS Scanned with CamScanner

Part (d) Intensity 1 Power Area J = P 0 x time and, - Pe W X At Energy as, 0.1J Energy Area = 0.01 m2 and 1 = lol wlm? From can Ex time 11 H Area orol seconds X 0,0 0.01 10-1 t = = 0:1 t orol seconds to time tapen by ooolm? energy trans tes through orol seconds a's CS Scanned with CamScanner