An aeroplane flying horizontal 1 Km above the ground is observed at an elevation of 60. After 10 seconds its elevation is observed to be 30. Find speed of the plane.

Asked by  | 12th Dec, 2011, 08:22: PM

Expert Answer:

When the elevation was 60, distance of the point of observation to the point on the ground
below the plane = 1xcot60 = 1/?3 km
 
Similarly when the angle becomes 30, distance becomes = 1xcot30 = ?3 km
 
So, distance travelled = ?3 -1/?3 km = 2/?3 km
 
time taken = 10sec = 10/3600 hr
 
hence speed = distance / time = 2x3600/10x?3 = 720/?3 km/hr = 415.7 km/hr

Answered by  | 13th Dec, 2011, 11:00: AM

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