- A40(√3 − 1) m/s
- B40(√3 + 1) m/s
- C80(√3 − 1) m/s
- D40√3 m/s
Step-by-Step Solution
Horizontal distances from O: 80 cot 45° = 80 m and 80 cot 30° = 80√3 m. The bird covers 80(√3 − 1) m in 2 s, i.e. 40(√3 − 1) m/s ≈ 29.3 m/s.
Answer: A) 40(√3 − 1) m/s
A bird sits on top of an 80 m tall tree. From a point O on the ground its angle of elevation is 45°. The bird flies horizontally straight away from O, and after 2 seconds the angle of elevation is 30°. Find the bird's speed.
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