Question

The angle of elevation of the cloud from the point 120 m above a lake is 30 and the angle of depression of its reflection in lake is 60 . Find the height of the cloud

Answer 1

the height of cloud is 240 m

Answer 2

$\huge\mathfrak\pink{Solution :-}$

Let AB be the surface of the lake and P be the point of observation such that AP = 60 m.

Let C be the position of the cloud and C be its reflection in the lake.

Then CB =

$\rm Draw \: PM \perp CBDrawPM⊥CB$

Let CM = h

$\therefore \rm CB = h + 60 m∴CB=h+60m$

$\rm In \: \triangle \: CPMIn△CPM$

$\rm \tan30 \degree = \frac{CM}{PM}tan30°=$

$\rm ➨ \frac{1}{ \sqrt{3} } = \frac{h}{PM}➨$

$\rm ➨ PM = \sqrt{3} h.......(i)➨PM=$

$\rm In \: \triangle \: PMC,In△PMC,$

$\rm ➨\tan60 \degree = \frac{C ' M}{PM}➨tan60°=$

$\rm ➨ \tan60 \degree = \frac{C'B + BM}{PM}➨tan60°=$

$\rm ➨ \sqrt{3} = \frac{h + 60m + 60m}{PM}➨$

$\rm ➨ \sqrt{3} = \frac{h +120m}{PM} .......(ii)➨$

$\rm☄from \: eq(i) \: and \: eq(ii)$

$\rm ➨ \sqrt{3}h = \frac{h + 120m}{ \sqrt{3} }➨$

$\rm \implies3h = h + 120m⟹3h=h+120m$

$\rm \implies3h - h= 120m⟹3h−h=120m$

$\rm \implies2h = 120⟹2h=120$

$\rm \implies h = \frac{ \cancel{120}}{ \cancel{2} } = 60m⟹h=$

$\rm \implies h = 60m⟹h=60m$

$\rm ➯ CB = h + 60m = 60m + 60m = 120m➯CB=h+60m=60m+60m=120m$

$⇾ \rm Thus,the \: height \: of \: the \: cloud$

$\: from \: the \: surface \:of \: lake \boxed{ \rm120m.}$