
Let AB be the observation tower and h be its height.
Also, let the ship be at C when the angle of elevation is 30° and at D when the angle of elevation is 45°.
The time taken by the ship to travel from C to D is 10 minutes and we need to find out the time the ship will take to reach B from D.
∴ tan 30º = AB/CB = h / CB = 1/ √3
⇒ CB = √3 x h
∴ tan 45º = AB / DB = h / DB = 1
⇒ DB = h
⇒ CD = CB – DB = (√3h – h) = h(√3– 1)
Now, as h(√3 – 1) distance is covered in 10 minutes, a distance of h is covered in = 13.66 minutes = 13 minutes 40 seconds