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

A helicopter takes off along the vertical with an acceleration `a = 3m

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