Aptitude - Height and Distance - Discussion

Discussion Forum : Height and Distance - General Questions (Q.No. 4)
4.
An observer 1.6 m tall is 203 away from a tower. The angle of elevation from his eye to the top of the tower is 30°. The height of the tower is:
21.6 m
23.2 m
24.72 m
None of these
Answer: Option
Explanation:

Let AB be the observer and CD be the tower.

Draw BE CD.

Then, CE = AB = 1.6 m,

      BE = AC = 203 m.

DE = tan 30° = 1
BE 3

DE = 203 m = 20 m.
3

CD = CE + DE = (1.6 + 20) m = 21.6 m.

Discussion:
18 comments Page 1 of 2.

Yazhini.M.R said:   1 decade ago
Since tan thetq= opposite/adjacent , tan 30= DE/BE ,

the value of tan 30 is 1/ root 3,

then DE/BE=1/root 3, then DE=BE/root 3,

thus 20 m is obtained.

since CD= CE+DE, 21.6 is obtained.

Anurag said:   8 years ago
Here DE/BE = 1/root3.

So, DE will be cross multiply by roo3 and BE will be multiplied by 1.
So, how come the value of DE is divided by root 3?

Priya58310 said:   8 years ago
Why they applied ''tan" what is the rule behind that?

Ravina said:   7 years ago
I too had the Same doubt @Priya.

Please clear the doubt of as.

Jatin007 said:   7 years ago
Applying tan because of we need to find DE.
So tan 30= DE/BE.
tan 30=DE/20√3,
DE=20√3*tan30( value of tan 30=1/√3),
So DE= 20.

So CD= EC+ED=1.6+20=21.6(answer).
(2)

Mahksh said:   7 years ago
There is no specific rule for this.

According to the situation we have to find this. Here, in this case, DE/BE i.e. perpendicular upon base means "tan".

So we take tan 30.

Monu_yadav said:   7 years ago
But the unit of 20√3 is not given in a problem. So,answer is None of these.
(1)

Akshaya Prasad Sahoo said:   7 years ago
Why are you using tan 30?

Lakshaya said:   7 years ago
Why be is Perpendicular to cd?

Seeli said:   7 years ago
Why they not use cos 30?


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