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An engine is moving towards a tunnel wit...

An engine is moving towards a tunnel with a constant speed.

To check its own velocity, the driver sends whistles twice at an interval of 2 minutes. The sound moves forward, gets reflected from the tunnel and again reaches to the driver. He listens two echoes of the sound, at an interval of 1 minute, if speed of sound is `300m//sec`, speed of the engine should be `:`

A

`50m//sec`

B

`75m//sec`

C

`100m//sec`

D

`125m//sec`

Text Solution

Verified by Experts

The correct Answer is:
B
`(2x)/(300)=t_(0) ......(1)`

Now in 2 minutes, the engine moves by `(u)(120)` so time taken by sound to reach the driver again is
`(2(x-120u))/(300)=t_(0)-120+60 ....(2)`
From equation `(1)` and `(2)`
`(2xx120u)/(300)=60`
`rArr u=(300)/(4)=75m//sec`
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