Ayesha is standing atop a vertical tower 200 m high and observes a car moving away from the tower on a straight, horizontal road from the foot of the tower. At 11:00 AM, she observes the angle of depression of the car to be 45°. At 11:02 AM, she observes the angle of depression of the car to be 30°. The speed at which the car is moving is approximately
Explanation:
At 11 am, the car is at C and Ayesha is at A. In △ABC, angle ACB = 45° Tan45° = 1 = ABBC ⇒ BC = AB = 200
At 11:02 am, the car is at D and Ayesha is at A. In △ABD, angle ADB = 30° Tan30° = 13 = ABBD ⇒ BD = AB√3 = 200√3
⇒ CD = 200√3 - 200 = 200(√3 - 1) = 200(0.732) = 146.4 m
∴ The car moved 146.4 m in 2 minutes.
⇒ Speed of the car = 0.1464 kms260 hours = 4.392 kmph.
Hence, option (d).
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