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Question

A bird was flying in a line parallel to the ground at a height of 2000 metres. Tom, standing in the middle of the field, he observed the bird making an angle of elevation 30. After 3 minutes, he again observed it with an angle of elevation of 45, the speed of the bird in kilometers per hour (3=1.732) is:

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Solution


Height of the bird from the ground =AB=CD=2000 m
Initially angle of elevation = 30
After 3 minutes, angle of elevation = 45

Let the distance when angle is 30 be d1 and when angle is 45 be d2
Now, from ΔABE
tan30o=ABBE
13=2000d1
d1=20003
And, from ΔCDE
tan45o=CDDE
1=2000d2
d2=2000

Now, distance travelled in 3 minutes, =d1d2=(200032000)m
=(2000×1.7322000)m
=1464m
Now, 1464 m=1.464 km

Thus, speed = distancetime
speed = 1.464360 km/hr
speed = 29.28 km/hr

279370_186710_ans_668d0e54ca1040b696a0c1202e4c16ed.jpg

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