Question

Boeing 767-400ER model airplane has two engines. Each engine can have a maximum thrust (mechanical force) output of 270 kN. When the plane is cruising at 739.64 km/h, the pilot decides to increase the speed to the typical 850.0 km/h. If drag on the plane is on average 28657 N, and the engines are engaged at 35.84% of their maximum thrust output, and the plane weighs 156892 kg, how long does it take to reach the new cruising speed? Include SI units Answer: 39.5 S x Check

Answer 1

Total thrust output by both engines =

2 * 35.84% * 270 kN = 193536 N

Average drag = 28657 N

Mass of plane = 156892 kg

By Newton's 2nd law,

Thrust - Drag = M*a

193536 - 28657 = 156892*a

Acceleration , a = 1.050908 m/s2

(for constant acceleration) change in speed = a * t

Change in speed = 850 - 739.64 = 110.36 km/h = (2759/90) m/s = 30.655556 m/s

Time it takes to reach new speed = change in speed / a = 29.1705 s