1.

A motor cyclist moving with 30 km/ h blows a whistle of 476 Hz towards a cliff. If velocity of sound is 1220 Km/h, the apparent frequency of the echo heard by him is :

Answer»

250 Hz
500 Hz
425 Hz
476 Hz.

Solution :When the ,MOTOR cyclist is approaching STATIONARY wall i. e. observer then
`v. = ((1220)/(1220 - 30)) 476 = 488 Hz.`
` therefore` FREQUENCY of reflected wave i.e., ECHO is 488 Hz and observer is moving towards it.
`therefore v.. = ((1220 + 30)/(1220)) 488`= 500 Hz.
hence the correct choice is (b) .


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