Question

QUESTION 6 OF 40 The angle of elevation of a jet plane from a point A on the ground is 60 degree. After a flight of 15 seconds, the angle of elevation changes to 30 degree. If the plane is flying horizontally at a constant height of 1500V3 metres, the speed of the plane in km/hr is​

Answer 1

Answer:

720 km/hr.Read more on Sarthaks.com - https://www.sarthaks.com/1021728/the-angle-elevation-plane-from-point-ground-after-flight-seconds-angle-elevation-changes

Step-by-step explanation:

Height of the jet plane = 1500√3 m  Initially the jet plane is at A and after 15 seconds flight at B. ED = x x, EC = y, where D is right below A and C is right below B  (the position of the plane after 15 secs). From ∆EBC, cot 30° =  y 1500 √ 3 y15003 ⇒  y 1500 √ 3 y15003 = √3 ⇒ y = 1500 √3 x √3 = 4500 m From ∆EDA, cot 60° =  x 1500 √ 3 x15003 ⇒  x 1500 √ 3 x15003 =  1 √ 3 13 ⇒ x x = 1500 m  ∴ AB = DC = Distance travelled in 15 seconds = y – x x = (4500 – 1500) m = 3000 m.  ⇒ Distance travelled in 1 second =  3000 15 300015 m = 200 m Hence speed of the jet plane = 200 m/sec =  200 1000 2001000 x 60 x 60 km/hr = 720 km/hr.