As observed from the top of a lighthouse 80 m above sea level, the angles of depression of a ship, sailing directly towards it, changes from 30° to 60°. Find the distance travelled by the ship during the period of observation. What was its
average speed if it took 1 minute to cover this distance?
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Answer:
Correct option is
A
92
Height of tower 80 m.
Two ships are at B and C.
Following the given figure, we can say
AC
AD
=tan60˚⇒
3
=
AC
80
⇒AC=
3
80
AB
AD
=tan30˚⇒
3
1
=
AB
80
⇒AB=80×
3
⇒AC+BC=80
3
⇒
3
80
+BC=80
3
⇒BC=80
3
−
3
80
BC=
3
160
BC=92.37 m
Nearest integer =92
solution
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