A straight highway leads to the foot of a tower. A man standing on the top of the 75 m high tower observes two cars at angles of depression of 30° and 60°, which are approaching the foot of the tower. If one car is exactly behind the other on the same side of the tower, find the distance between the two cars. (use 3=1.73)
Solution
1
Tower AB = 75 m with two cars at P and Q, angles of depression 60 degrees and 30 degrees
+1 mark
2
AB = Height of tower = 75 m. P, Q are positions of cars. ∠XBQ=∠BQA=30°, ∠XBP=∠BPA=60°
+0.5 marks
3
In △APB: tan60°=AP75⇒AP=375=253
+1.5 marks
4
In △AQB: tan30°=AQ75⇒AQ=753
+1 mark
5
Distance between the cars =PQ=AQ−AP=753−253=503=50×1.73=86.5 m
+1 mark
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