move apparent frequency equal to 11 12 of the original frequency 1 V 2 2 2V 3 V 4 4 V 11 31 A whistling engine is approaching a stationary y observer with a velocity of 110m s The 44 velocity of sound is 330m s The ratio of frequencies as heard by the observer as the engine approaches and receedes is 1 n 10n 2 n 03 n 0 In 4 n 0 In a source of sound is travelling towards stationary observer The freqency of sound heard by the observer is 25 more than that of the actual freqency if speed of sound is V that of the source 2 4 1 1 4 3 3 3 6 is 4 2 1 1 V 5 2 V 4 3 V 3 4 V 2 38 Two aeroplanes A and B are moving away from one another with a speed of 720 kmph 45 A truck blowing horn of frequency 500 Hz travels The frequency of the whistle emitted by A is 1100 Hz The apparent frequency of the whistle as heard by the passenger of the aeroplane B is velocity of sound in air is 350 ms towards a vertical mountain and driver hears echo of frequency 600Hz If velocity of sound in air is 340m s then speed of truck is 1 31 m s 2 41m s 3 51m s 4 21m s KEY 1 300Hz 2 400Hz 3 500Hz 4 600H 39 An engine is moving on a circular path of radius 100 metre with a speed of 20 metre per second The frequency observed by an observer standing stationary at the centre of circular path when the engine blows a whistle of frequency 500 Hz is 1 more than 500 Hz 2 less than 500 Hz 3 500 Hz 4 no sound is heard perceives the sound n n If the velocity of sound in air is 300 m s then 40 The frequency of a radar is 780 MHz The frequency of reflected wave from an aeroplane is increased by 2 6KHz The velocity of the aeroplane is 1 2 km s 2 1 km s 3 0 5 km s 4 0 25 km s 41 An observer moves towards a stationary source of sound with a velocity one fifth of the velocity of sound The percentage increase in the apparent frequency is 1 5 2 20 3 zero 4 0 5 4 A train is moving at 30ms in still air The frequency of the locomotive whistle is 500 Hz and the speed of sound is 345 ms The apparent wavelengths of sound infront of and behind the locomotive are respectively 1 0 63 m 0 80 m 2 0 63 m 0 75 m 3 0 60 m 0 85 m 4 0 60 m 0 75 m 1 2 7 1 13 3 19 4 25 2 31 1 37 4 43 2 43 A vehicle with a horn of frequency n is moving with a velocity of 30 m s in a direction 2 3 2 k 2 1 3 3 4 2 5 1 6 4 8 2 9 1 10 2 11 2 12 1 14 2 15 2 16 1 18 2 22 2 28 3 34 1 40 3 20 1 26 1 32 3 38 1 44 1 y Acos 2ant 22 21 3 27 2 2 V part max GR IFF MAINS MATERIAL 33 4 39 3 45 1 HINTS V n 270x 2 17 4 23 3 29 2 2TX cos 2n 2n 2 2 Ap 1080x 35 4 41 2 Use cos 0 a y 6m 2 sin 2n 31 x 24 2 30 2 36 4 42 2 1 cos 20 2 3 x N2 N where N is no of waves and V n n 4 Vwave A 4 na T 6nrad Ab 180 2 n V Ax AMARAVATI IT JEE ACADEA