An air is flying at a heith of ` 3500 m` above the ground, If the angle subtended at a ground observation point by the air craft positions `10 s` apart is ` 30 ^@` while passing over his head, what is the speed of the air caraft ?

Explanation

In Fig. 2 (d). 40, (O) is the observation point at the ground ` A` and ` B` are the positions of the air craft for which ` /_AOB = 30^2`. Draw a perpendicular (OC) on ` AB` . Here, ` OC = 3500 m` and ` /_ AOC`
` = /_COB= 15^@``. Time taken by air craft from (A) to (B) is ` 10 sec`.
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In ` Delta OAC, AC= OC tan 15^@`
` = 3500 xx 0.2695`
`= 937. 65 m`
` So,` AB = 2 xx AC = 2 xx 937. 65 = 1875.3`.
:. Speed of air craft, ` v= ( 1875.3)/( 10) = 187.5 ms^(-1)` .