An aeroplane flying horizontally 1 km...

An aeroplane flying horizontally 1 km above the ground is observed at an elevation of `60o` . After 10 seconds, its elevation is observed to be `30o` . Find the speed of the aeroplane in km/hr.

`120sqrt3` km/hour

`240sqrt3` hour

`250sqrt3` km/hour

none of these

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