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A helicopter is flying horizontally at 55m/s towards a cliff. When the pilot is 1500m...

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A helicopter is flying horizontally at 55m/s towards a cliff. When the pilot is 1500m away from the cliff he sounds a horn. The speed of the sound in air is 345m/s.

a) How long will it take the pilot to hear the echo?

b) How long would it take to hear the echo if the helicopter is moving away from the cliff at the same speed?

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Posted (Answer #1)

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a. Let pilot hear echo after ' t' sec.

so distance travelled by sound in t sec = 345t m.

distance travelled by helicopter in t sec towards cliff = 55t

Thus

2 x 1500 -55t= 345t

400t=3000

t=7.5 seconds.

b. helicopter is moving away from the cliff . Let pilot hear echo after ' T' sec.

so distance travelled by sound in T sec = 345T m.

distance travelled by helicopter in T sec away from cliff= 55T

Thus

2 x 1500 +55T= 345T

290T=3000

T=10.34 Sec.

 

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