AI Mentor

Check Your IQ

Free Expert Demo

Try Test

Courses

Dropper NEET Course Dropper JEE Course Class - 12 NEET Course Class - 12 JEE Course Class - 11 NEET Course Class - 11 JEE Course Class - 10 Foundation NEET Course Class - 10 Foundation JEE Course Class - 10 CBSE Course Class - 9 Foundation NEET Course Class - 9 Foundation JEE Course Class -9 CBSE Course Class - 8 CBSE Course Class - 7 CBSE Course Class - 6 CBSE Course

Offline Centres

A 20 m long flagstaff stands on a tower. At a point on the level ground the angles of elevations of the foot and top of the flagstaff are $30 °$ and $60 °$ respectively. What is the height of the tower?

see full answer

Your Exam Success, Personally Taken Care Of

1:1 expert mentors customize learning to your strength and weaknesses – so you score higher in school , IIT JEE and NEET entrance exams.

An Intiative by Sri Chaitanya

20m

10m

15m

25m

answer is B.

(Unlock A.I Detailed Solution for FREE)

Best Courses for You

JEE

NEET

Foundation JEE

Foundation NEET

CBSE

Detailed Solution

Given that,
The height of Flagstaff =20 m long,
Angle of elevation of the foot and top of flagstaff =

30 °

and 60

° .

We draw diagram,
Question Image

We use the trigonometric identity,

tan θ = p e r p e n d i c u l a r b a s e

We get the value of BC from

Δ A B C

tan 60 ° = A B B C ⇒ 3 = A B B C [∵ tan 60 ° = 3] ⇒ B C = A B 3

⇒ B C = A D + D B 3 ..... (i)

We get the value of DB from

Δ D B C

tan α = D B B C ⇒ tan 30 ° = D B B C ⇒ D B = tan 30 ° × B C ......... (i i)

Substituting the value of BC in equation (ii),

⇒ D B = tan 30 ° × B C

⇒ D B = 13 × A D + D B 3 [∵ tan 30 ° = 13]

⇒ D B = A D + D B 3

⇒ 3 × D B = A D + D B

⇒ 3 D B − D B = A D ⇒ 2 D B = A D ⇒ 2 D B = 20 ⇒ D B = 10

Thus the height of tower is

m.
Therefore the correct option is 2.

Watch 3-min video & get full concept clarity

courses

No courses found

Result Producing online coaching for JEE/NEET of south India

Largest All India Test Series for JEE/NEET

Best Online Course for IIT JEE

Best Online Course for NEET

Best Online Course for CBSE

Ready to Test Your Skills?

Check your Performance Today with our Free Mock Test used by Toppers!

Take Free Test

Get Expert Academic Guidance – Connect with a Counselor Today!