Question

An aeroplane flying at a constant speed, parallel to the horizontal ground, $\sqrt{3} \, km$ above it, is observed at an elevation of $60^{\circ}$ from a point on the ground. If, after five seconds, its elevation from the same point, is $30^{\circ}$, then the speed (in km/hr) of the aeroplane, is :

• A. 1500
• B. 1440
• C. 750
• D. 720

Answer 1

Answer: (B)

1440

Answer 2

$M \,5 \,sec =2 \,km$ Speed $=2 / 5 km / sec$ $=\frac{2}{5} \times 60 \times 60$ $=1440 \frac{ km }{ hr }$