Question

plz silver this best answer will be marked brainiliest...
A moving boat is observed from the top of a 150 m high cliff moving

away from the cliff. The angle of depression of the boat changes from

60° to 45° in 2 minutes. Find the speed of the boat in m/ℎ.

Answer 1

Answer:

1905 km/hr

Step-by-step explanation:

From figure:

Given, AB = 150 m, ∠ACB = 60°, ∠ACB = 45°.

(i)

cot 45° = AD/AB

⇒ 1 = AD/150

⇒ AD = 150 m.

(ii)

cot 60° = AC/AB

⇒ 1/√3 = AC/150

⇒ AC = 150/√3

          = 150/√3 * (√3/√3)

          = 150√3/3

          = 50√3

          = 86.5 m

Now,

CD = AD - AC

     = (150 - 86.5)

     = 63.5 m

Given that it takes 2 minutes = (2/60) hours = (1/30) hours.

∴ Speed of the boat = (63.5/1/30) m/hr

                                 = (63.5 * 30) m/hr

                            = 1905 km/hr.

Hope it helps!