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vikram1989 (0)

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Prisoners trying to escape.





To try and find the height of the wall so that they can determine how many bed sheets they can tie



togethr to make their rope , the full height of the wall at the crossing point P.





Each sheet contributes 2.1m to the length of the rope.





From point A in the prison yard,due south of P,a prisoner measures the angle of elevation of P



to be 31 degrees





From poit B in the prison yard 15 meters due east of A,he finds the angle of elevation of P is



25 degrees





The eye of the prisoner is 1.7m  above the ground.





Calculate the vertical height of the wall to the nearest 0.1m,and hence determine the number of



sheets needed for the rope.


Check : Answer is 7.2 meters and 4 sheets.


Thanks in advance.


    
krishna.gopal (2149)

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Let The point below P in plane of eyes of prisioner at A and B is Q
Let PQ=h
and
AQ=b
From first
tan(31)=h/b
By pythagorus theorm
BQ=sqrt(b^2+15^2)
Therefore
tan(25)=h/sqrt(b^2+15^2)

Using the two equations solve for h and b.
Height of point P=h+1.7 meters

Krishna Gopal Singh
B.Tech Chemical Engg
IIT Delhi 2002
Currently doing PhD from IIT Delhi
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vikram1989 (0)

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Thanku brother .That was exellent i got the answer,


i think this was a typing mistake

By pythagorus theorm

BQ=sqrt(b^2+15^2)


i think it shud have been


By pythagorus theorm

BQ=sqrt(15^2-b^2)


Any ways thanks once again.


Bye.

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