QJEEM21Mac207: JEE Main 2021 Mathematics - Class 12 JEEM21Mac207 Solution: The angle of elevation of a jet plane from a point A on the…

Question

Verified Solution • 2025–26 Session moderate

The angle of elevation of a jet plane from a point A on the ground is 60

^\circ

. After a flight of 20 seconds at the speed of 432 km/hour, the angle of elevation changes to 30

^\circ

. If the jet plane is flying at a constant height, then its height is :

Accepted Answer

v = 432 \times {{1000} \over {60 \times 60}}

m/sec = 120 m/sec

Distance AB = v

\times

20 = 2400 meter

In

\Delta

PAC

\tan 60^\circ = {h \over {PC}} \Rightarrow PC = {h \over {\sqrt 3 }}

In

\Delta

PBD

\tan 30^\circ = {h \over {PD}} \Rightarrow PD = \sqrt 3 h

PD = PC + CD

\sqrt 3 h = {h \over {\sqrt 3 }} + 2400 \Rightarrow {{2h} \over {\sqrt 3 }} = 2400

h = 1200\sqrt 3

meter

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