An aeroplane flies horizontally at a height of 1500 m. From a point on the ground, its angle of elevation changes from 60° to 30° in 10 seconds. Taking √3 = 1.732, what is the speed of the aeroplane in km/h?
Correct answer D. 623.52 km/h
Explanation
Horizontal distance covered = 1500(√3 - 1/√3) = 1000√3 = 1732 m in 10 s, i.e. 173.2 m/s. In km/h: 173.2 x 18/5 = 623.52 km/h.
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