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A helicopter takes off along the vertica...

A helicopter takes off along the vertical with an acceleration `a=3ms^(-2)` and zero initial velocity. In a certain time `t_(1)`, the pilot switches off the engine. At the point of take - off, the sound dies away in time `t_(2)=30s`. Determine the velocity v of the helicopter `("in "ms^(-1))` at the moment when its engine is switched off, assuming that the velocity c of sound is `320 ms^(-1)`.

Text Solution

Verified by Experts

The correct Answer is:
`80 ms^(-1)`
Let t= time of accelerated motion of the helicopter.
Distance travelled by helicopter
+ Distanace travelled by sound
`rArr (1)/(2) xx 3 xx t^(2) =320 (30-t)rArr t=(80)/(3)sec`
Final velocity of helicopter
`v=u+at =0 +3 xx (80)/(3)= 80 m//s`.
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